So much for a few design tweaks.
Here’s what I have so far for a 1/19 (4 studs wide) speeder. The top and front of the body, the bottom engine, and the controls are largely unchanged from the kit. The interior, bottom, and sides of the body, the top engine, and the saddle mounting are all completely different. The body’s one stud longer than the original, to get it closer to scale length. I did reuse the 4×4 wedge panel on the sides, which do not hinge. There are no provisions at all for opening up the body — there wasn’t really room inside for even the suggestion of engines to look at.
There’s a couple of holders where a net can be attached to the left side (but not in LDD), and they can be used to clip Rey’s staff to the speeder too — a staff which also got redesigned, since the minifig scale staff was too small for this model.
I did change the front grille to black (not that all the colors here are what I would use in a physical build). No oval rim though. The stud shooters have reverted to “directional steering exhaust nozzles”, executed similarly, I think, to Andrew Becraft’s model.
If I know me I’ll probably fiddle with this a bit more, but unless I find a serious fundamental flaw, which is entirely possible, I don’t think I’ll make any major changes. As for building it, well, not very soon, but maybe after Christmas I will.