I agree. My fear is that if I bring the filament outlet close enough for the mk8 to print flexibles, it will stop fitting the mk7 or other drive gears. And so on. That precision of fit is really hard for a design to accommodate multiple drive gear sizes.
The only good solution I've thought of is using the M4 nut version of the arm, and bringing the PTFE tube all the way back to the drive gear so you can adjust the spacing to suit each drive gear.