alt Hacker NewsThe bend angle of the tube that forms the seat support down to the legs seems like one of their major adjustment points for comfort and efficiency so I don't think you could have a similar setup. These are essentially semi-custom not a simple size based product like a bike. The extra adjustments are important because the users are in them many more hours a day so small problems can cause long term issues.
Their configurator has a very good model of what the chair will look like and you can see just how many knobs you can tweak and how that requires changing the core layout of the frame in a way that makes the kind of sizing system just not feasible. Scroll down on the Frame page to get to the fit sliders.
https://notawheelchair.com/pages/configurator
edit: Did the math and there's something like 25k different configurations they're selling before accounting for paint colors, just in the frame measurements. Granted, that's not accounting for the improbability or incompatibility of some parameter sets but that's still going to be a couple thousand different configs to build and stock. It doesn't work like a bike.
On a bike you have a little bit of flexibility due to the way the seat post works. Both in how the seat attaches and adding curves to the post, particularly for triathletes who like to favor their hamstrings over their quads, and sit considerably farther forward than any 'normal' cyclist would.
I know I've seen wheelchairs where the back was a tube that went into a tube. If you put the curve in the replaceable part you get more adjustment but less support. Generally the tolerances on bikes are very tight and medical equipment seems to be all over the place.