Six jours,
Ignore this if you don't want any more ideas, but I've been imagining something like this: a unicrown fork with straight blades or at least very low offset and decent diameter down to the bottom. At the bottom, joined to the tube using perhaps gussets in addition to the normal dropout attachment, a horizontal dropout with a forward-facing slot. No fender to minimize issues with changing tire /fork clearance. The slots on both sides have graduations to facilitate aligned and repeatible installations. QR or bolted-axle pressures hold the wheel in place, just like with standard dropouts. If the wheel is not stable, tending to ride backwards in the slot, an alignment screw in the back of each slot, running forward to stop the axle. Axle still obviously needs to be clamped.