Doesn’t matter with reliable brake mechanism?
Yeah, vaguely recall link for narrow ones shared on the ebrake topic. Sounds good, am dubious about the electronics working reliably 100% for 100% situations 
EDIT: Found Paul’s post with link to 3/8" wide springs, there’s a bunch looks like some experimenting needed if trying this out.
wrt inserts. Personally prefer design to just require nuts and bolts if possible. Simpler/faster to assemble, just use medium threadlocker.
Was imagining bulk of the coil rides with the moving Steppers, so only the end is attaches to modded Z Belt Holder.
Between hotend and PTFE needing to flap around, we need ~120mm height Lid anyway, so, guessing there’s plenty of room up top, especially if XY steppers are at the back?
There seems to be some space. Would repositioning Z linear rails to be on front (or rear) face of the upright extrusion enable simpler CNC’d plate based Z Posts? Belts stay pretty much where they are. Can Z Post end up just being a CNC’d/laser cut plate, with no/minimal printed part(s)?
If Linear rail block ends up being proud of extrusion. Not a problem if open frame. If someone wants to enclose, they can make cutouts in their panels, and optionally print/CNC a shroud to cover where the rail blocks are moving, if they care even. If people are are wanting fancy pants exterior polycarbonate panels, then they also have the budget to build 2040 frame.
Could avoid 2040 frame and cutouts in panels by using standoffs. But don’t think standoffs between panel and frame is good, because direct contact between true square panels and frame will help with squaring frame, rigidity, etc…
If people have budget for 2040 frame, they might want to experiment with having Y rail horizontal on top (kinda like prusa xl) too assuming Z Steppers don’t end up on top.
EDIT: Would isolating the Z extrusions with linear rails attached from panels reduce vibrations/noise too?