I have had my eye on a desk with motor/s, but my previous one did not have this feature.
I am guessing that if the legs are joined by a solid enough crossbar, then sag will not be a problem.
The desk I consigned to the skip two weeks ago looked like this (without motors or the third leg, though there were screw holes in the table top that would have corresponded to this third leg).
UPLIFT Curved Corner Standing Desk, 3-Leg
The "thin side" was good enough for my iMac, keyboard, mouse and me. My printer went onto the "wide side" and there was plenty of rom for bits and pieces, so something around 28"/ 70cm constant depth would be OK.
My SO suggests I get something custom made. Tempting, but dangerous...