Has there been any thought as to ignoring the XY endstops and moving to a hard homing approach?
By hard homing I mean "softly" crashing the carriages into the end of travel by giving a slightly larger than the possible x-y travel g-code. At the end of the move you know exactly where the X and Y is. The steppers just skip steps once the carriage hits the end of travel.
Since the steppers we (or at least I) use are relatively weak it wouldn't hurt the machine any, especially if some sort of semi-soft bumper was provided. Also, the XY homign accuracy really doesn't have to be that great since most people aren't homing mid print, or printing within .5mm of the print envelope.
Just a thought...