So I wanted a quick change X carriage that allows me to leave alone the bushings and rods, as much as possible.
Also, I am printing PLA, and there are just too many reports of melted/warped/softened X carriages floating around to be at ease with a PLA carriage. However, this should not be a problem with the bushing holders because of the heatsinking effect of metal.
I like GregFrost's three bushings X-carriage thingiverse.com/thing:9869 , but I think the side with two bushings should be positioned near the belt, and not the opposite way.
Note: this mod adds about 6 mm to the extruder base height. As I have verified with use, this does not interfere with "standard" hotends (I'm using ParCans design).