OK Here's an updated list:

maunakea? (post #75 )
12boy? (post #121 )
towndock (post #142 ) (drawings sent)
Richbiker (post 223) (drawings sent)
tikman1313 (post #241 ) (drawings sent)
shroom (drawings sent)
plus 1 or 2 more from private correspondence. Question marks are still to be confirmed either way. Don't worry if you can't make this batch, I have built up a good relationship with the builder and am able to apply some price pressure even if you want to do a single buy later, especially as we now have a lot of drawing to suit the majority of choices.

In order to hammer down frame size, each party will need to furnish either their preferred frame size top tube length or something similar so we can spec top tube length. For reference, the original Xootr has a 55cm top tube. That is essentially a size medium, perhaps good for medium sized people. Myself I am 5'10 so I prefer something longer, so for my own one I added an inch to that, for 57.5cm which is spot on. The previous batch most people went with 57.5cm, save for one at 55cm and one at 59cm.

Then the preferred wheel size is next plus the preferred braking system(s). Also the rear dropout width, the dropout style and the belt joint, if preferred.