It doesn't exist yet, but we could use CT-mode with a modified MMU or ERCF unit.
For multicolor prints we'd cut the required filament-length right at the MMU and feed it to the extruder without all the time- and material wasting full_retraction and purge stuff.
Problem would be to sync the toolhead motion with the filament feed and that would probably be easier if the MMU would work in constant torque mode 🙂
Everytime we cut the filament off and reposition the MMU feeder towards the next color, we'd see a gap in the feed.
But in CT-mode we quickly close this gap, once we feed new filament.
It would require a closed loop MMU-motor and/or a filament monitor to keep track of the feed. A second filament monitor (switch) on the toolhead would tell us, when the first piece of filament feed arrives, so we can start the actual print.
It would require working with dual-gcode stream:
Best way to start a print would be a single color bottom layer.