Second.
I have no interest in multi-hole cranks with current pedals, for the reasons you mention, but would be very interested in that.
Presumably the current systems you mention are a single type of pedal designed to work with standard cranks (a link would be handy?) - how about also going a bit more lateral and making a crank with a QR pedal insert (which takes standard pedals, so letting the rider use their preferred option). I can even see the possibility here for a continuously variable option - if not necessarily changeable on the fly. The big problem I can see is eliminating the slop - some sort of taper fit would presumably be required. Or maybe something adapted from through-axle securing systems on bicycles.
One blade unicycle
How about a uni with one blade frame? I would try to convince Triton to build a custom lefty if there was a suitable hub 
A solution looking for a problem?
Why not modify a Lefty fork and wheel? It could probably be done if you had access to a machine shop. A guy I rode with in Oregon had a similar idea, not sure if was serious about producing it, but seeing as you need a custom hub and bearing, that makes it a little more complicated.
I would also expect that the oversized hub, bearing, and one legged frame would end up being heavier than standard hub and fork, though it would look cooler 
The problem with a threaded QR adaptor that uses existing cranks is you would either have to offset the pedal or have a different pedal spindle. White Bros has a QR crank that allows the use of any pedal, but it’s a single hole and is square taper. Here’s a link: http://whiteind.com/cranks/quickreleasepedalcrank.html
Maybe an insert could be made that would fit in place of the Moment pedal inserts? I’m thinking of a brass sleeve on the (male) pedal side that has internal 9/16 threads for a standard pedal which is screwed onto the pedal spindle. Then on the crank side there is a (female) brass sleeve which replaces the Moment pedal inserts. On the end of the male insert there is a grove for a U Clip with a safety ring, so all you do is unclip the pedal, swap holes, and reclip the pedal.
Funny, I actually didn’t really look at the White Bros version until just now, and it’s the same thing I had in mind 
So if a crank without inserts were “overdrilled” to accept an insert, then this could work on any crank or if a different insert were developed for an existing crank that has a pedal insert…
It’s been tried many times over the years (link above goes to an early example). Consensus is that it’s unrideable other than as a novelty, but this was a free-as-in-unhindered freewheeler.
The idea of a drag clutch / brake might first be tested on a platform such as the one above. It might make the ride a little easier.
Wow, way to start a fire, then throw a wet blanket on it…
Yeah, I could see that. You need the resistance and act of pedaling to help keep your balance. It is funny that the Green Machine is mentioned as a way to frankenuni one. We have a GM and that was the first thing I thought was that is looked like a uni laying down on the ground.
Who says the insert needs to be round? Make it shaped like a peanut with the pedal threaded into one end and the same shape cut into the crank arm. Then you could easily adjust the effective length by flipping it around and re-inserting it into the crank. The ‘peanut’ also gives the sliding clip more purchase by having longer sides…
Sounds like we need someone with a CNC… The advantage of a round design is that it’s pretty easy to drill and tap a hole, while CNCing a peanut shaped one is a lot harder.
So i was riding muni why dont we have cranks with more Q than moments? i like having alot of Q fator makes it feel like i have more control
Variable Length Cranks!
Probably been thought of already but why not try some cranks that govern automatically how long they need to be.
If the pedal was mounted in a rail that slid up and down the length of the crank and there was a spring to provide some resistance then when you need the length “as your standing on the pedals” , you overcome the spring, when you move back to less power needed the spring pushes the pedal back towards the centre of the crank.
Make sense? In my head it kind of does, but how you’d make it I don’t know.
One problem with that idea is that you are not only pushing on the pedels when they are directly vertical and down, but actually the whole time they are rotating.
You could put a pivot point in the crank arm.
E.g. Assume a 165mm max length. At ~125mm from the hub, you have the pivot and a smaller ‘elbow’ that will extend from slightly bent (putting the pedal ~135mm from the hub) to fully straight @165mm. A strong spring would pull the elbow bent. Mashing down hard on the pedal could open the elbow to its full length, and releasing pressure (such as on the upstroke) the spring would bend the elbow again returning the crank to it’s shorter position.
Obviously I’m just throwing stuff at the wall to see what sticks, but it seems feasible. It would take some getting used to with the cranks ‘moving’ a bit and the non-circular pedal rotation, but it might work… 
Why not have variable cranks that don’t adjust automatically depending on pressure, rather they can be manually varied? You can maintain a circular motion that way and the pedals could hopefully be more rigid.
Thinking of how to manually change the length… You could have a cable attached to the frame and the crank bearing (to avoid tangling with feet and pedals) that may tighten and pull the outer parts of the crank further in, thus shortening the crank. It all seems really odd. I wonder how much it would actually help to ‘gear’ the thing?
They exist, check out ISIS Try All cranks, MOnte, etc… they have upwards of 30-35mm offset, compared to 10-15mm for Vebtures and 25mm for Moments.
I also like high Q, esp with shorter cranks.
Some great ideas out there, anyone want to tackle a prototype?
That might be one way to make a variable length crank you adjusted when you stopped. I reckon any on-the-fly variable length crank is pretty much a non-starter though - one using a spring to adjust automatically certainly is.
I really like the idea of adjustable crank lengths. A quick google search brought up the following:
http://www.behance.net/gallery/ADJUSTABLE-LENGTH-OF-BICYCLES-CRANK-ARM/4427387
http://www.bikecyclingreviews.com/A_Different_Leg_Length_Problem.html
So this is an idea that is doable and would be super awesome!
Parts of the conversation made me think of that :
I don’t know what was the result with use, I should ask Romain…
If you want more q factor get one of the Nimbus 125mm spaced hubs and a Oregon frames to fit the wider hub. Or like NurseBen said get high q bike cranks (although they pretty much come in long lengths by unicycle standards.)
Also the wider you go the more pedal strikes you’ll get when riding narrow trails!
Saying that I prefer Moments over Ventures the higher q means you don’t hit your shoes as much + as you said feels like you have more control.
I really like your ideas about larger bearings and axle- those would be great improvements.
As for what new products I’d like to see made:
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A round crown KH muni frame’s in 26 and 29
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A comfier seat- the custom flat carbon based seats look better to me!
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I’d like to see Nimbus make their dominator 2 rim 47mm wide- perhaps with some drilling to keep the weight down
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Some sort of guard such as this: Trials Bikes at TartyBikes - The World's Leading Online Bike Trials Shop but specificaly designed for muni’s.
That quick release system has been around for a while, it’s more of a road bike style for bikes that are folded for transport. I read that they are fragile. They also seem to set the pedal away from the cranks.
There is another version that has a QR on the side, made by MKS I think, but it has that same offset, thoug it may be more durable.
I’m goi g to dismantle some Moments and take a look at the insert sizing, just to see if it is doable with some custom machining. I’d love to get ahold of some White Bros pedal inserts without having to buy the cranks.