A few weeks ago I saw somethin similar on an old Penny Farthing. Looks reasonable to me.
In addition, also the seat hight would need to be adjusted to. I think, not many riders change crank length during a ride. But I also don’t think, this is what they were meant for. As finnspin said: finding the perfect length for fast road riding is the scenario where they would come in perfect.
For changing lenth on the fly, things would need to work tool free to really be used much.
A few years back, I had a discussion with Kris Holm on quick-release-pedals. He then got samples from Wellgos QRD system - both, version I and II. We figured out, that version II is a little bit too wide for the hole distance of the existing dual hole cranks and Version I would be narrow enough, but can’t be screwed in due to the knob. If one could implement the mechanism of version I into the cranks, that would work great. I think, only with quick-release-pedals would multihole cranks be used regularely for changes on the fly.
On the other hand: if one could make those Qu-Ax cranks QR …
Im not so fond of the quick release clamps on the seat. You always have to sort of find the balance between screwing the bolt with an allen key and at the same time be able to close the clamps all the way. So then just a bolt that you can adjust with the Allen key that everyone already rides with would be sufficient.
Pedals are a bit more cumbersome. There I worry more about damaging the threading and you can’t unscrew it with an Allen key, so it requires more tools to bring along.
Anyways the chance of having to change the seat is bigger, because a UPD could twist it and occasionally I do set it higher or lower when the height doesn’t feel right that day.
QRD trials here.
The MKS EZY work better (also discussed a bit further down), but in the end I (and almost everyone else I think) decided that the additional Q-factor made them not really useful, although I didn’t try them on zero-q at the time as I didn’t have any.
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I think it’s the bolt that would fail, which is a scenario I would personally not want to risk. It may snap, or it may come loose. In that scenario, I also see the risk of damaging the crank side in Muni, where there may be strong forces on the pedals before you notice.
I’m pretty sure for Muni, you’d need a redesign and a lot more testing. One step after the other, let’s see how much people like it for it’s intended use first.
Same for me, that’s why I don’t run multi hole. But the intend here is to enable fine adjustment, not necessarily changing more frequently.
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I think multi hole is fine, then I don’t need to have 2 sets of cranks and you can more easily figure out what works best for you.
This is true for non-expert riders. Finn is an expert, he knows what works for him. No need for multi-hole cranks in that case 
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Absolutely! In fact, that’s what I do when I decide to climb a hill with an ungeared unicycle.
With my ungeared 36", I did it with an ISIS axle and 117/138/159 triple cranks.
These cranks tempt me for my freewheel 29", but I’m primarily interested in the extreme lengths (145 and 105 mm).
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The more I think about it, the more I see the range as a problem. Should be something in the 30-50mm range for our tiny cranks friends…
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I love these. From what I surmise Quax is not available here in the USA. One-day I would like to get a Quax 27.5 RGB a set of these cranks on it would be awesome. It will be interesting to hear of real world testing by unicyclists.