MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
I figured you'd add your prusa belt attachment method to the open-x carriage rather use the open-x directly. (I agree, I'm not fond of the current open-x belt attachment either.)
The single dangling bearing is fine, in fact it could probably be removed altogether - gravity plus extruder weight holds the carriage down fine (although maybe if your filament spool was high friction and causing pulling up on that side of the carriage it could be a problem).
The regular mendel
carriage really sucks for accessibility, whenever I wanted to remove my extruder I found myself cursing trying to poke at nuts past the rods on the inside.