Although it seems so obvious to me that unicyclists use short cranks because our limit is velocity, not power.
As a reminder, power is what moves us forward, and it’s the product of strength multiplied by cadence/speed/velocity.
To gain velocity, you need to train hard. Whereas you can gain in strength, just by using longer cranks.
Once you’re using the optimum crank length, you also need to train hard to gain strength. 
It’s obvious but that’s a good point 
However, even with 1.7:1 or 1.8:1 ratios, we would still be far away from standard bikes. Let’s toy with the Total Gear Ratio concept of @Klaas_Bil!
I’m not an expert, but I have read that bikes have chain rings consisting of about 50 teeth, and smallest cogs on a cassette have around 12 tooth (more or less, depending on the rider), making a gear ratio of ~4.1. Let’s say you don’t want to use only the smallest cog, but one that’s a bit bigger. Let’s say 16 teeth => gear ratio of 3.125 - that’s an arbitrary number, but it seems to match what I’d ride on a road bike.
Let’s enter these numbers into a spreadsheet, and voilà!
| Wheel size (inches) | Wheel radius (mm) | Gear ratio | Cranks length (mm) | Total Gear Ratio (= Wheel Radius x Gear Ratio / Cranks Length) |
|---|---|---|---|---|
| 28 | 223 | 3.125 | 175 | 3.99 |
| 28 | 223 | 4.1 | 175 | 5.23 |
| 36 | 287 | 1.54545455 | 110 | 4.03 |
| 36 | 287 | 1.54545455 | 127 | 3.49 |
| 36 | 287 | 1.54545455 | 145 | 3.06 |
| 36 | 287 | 1.54545455 | 150 | 2.96 |
| 36 | 287 | 1.54545455 | 160 | 2.77 |
| 36 | 287 | 1.7 | 110 | 4.44 |
| 36 | 287 | 1.7 | 127 | 3.84 |
| 36 | 287 | 1.7 | 145 | 3.37 |
| 36 | 287 | 1.7 | 150 | 3.25 |
| 36 | 287 | 1.7 | 160 | 3.05 |
| 36 | 287 | 1.8 | 110 | 4.70 |
| 36 | 287 | 1.8 | 127 | 4.07 |
| 36 | 287 | 1.8 | 145 | 3.56 |
| 36 | 287 | 1.8 | 150 | 3.45 |
| 36 | 287 | 1.8 | 160 | 3.23 |
If you wanna match an “easy” TGR of a bike on a Schlumpf G36er, you’ll have to ride with 110’s. Good luck with that 
Let’s now say we have a new hub with 1.7 or 1.8 gear ratio. As you can see, while 150’s or 160’s may be a bit better than 145’s on a Schlumpf hub, they barely match with 127’s.
Fun fact: 160’s with a ratio of 1.8 should make you as fast as you’re already on a Schlumpf G36er with 145’s.
Although long cranks may help to get the maximum power of your legs as you can use more muscles, I’m really not sure people will go longer. I may be biased and speak only for myself, but I think unicyclists find it strange to spin long cranks. We tend to prefer smaller ones, as that’s what we’ve learned on.
I like numbers, but applying cyclists’ ratios to unicycling is abstract.
Unicyclists have the ability and need to pedal at a wide range of cadences, whereas cyclists always pedal at the same cadence.
I find the wheel/crank ratio too simplistic. For the same ratio, you always go faster with the bigger wheel (up to a certain point, which one?). On the other hand, for the same wheel size, you don’t necessarily go faster with shorter cranks. For example, on my G36, I trained with 138mm cranks, and I was slower than with 145mm.
Rather than a spreadsheet, I see it as a chemical reaction where you have to add the right amount of strength and cadence, so that once the chemical reaction is over, there’s nothing left. 
It seems to me that the pedals are very far apart each other, a huge Q-factor, if you want. That‘s something that puts me off a bit. And while the frame looks quite pleasing, it also looks pretty massive (read: heavy). On the other hand, the solution with chains is a lot lighter than a geared hub…
