@Phaedrux Parsing gcode files to use M201.1 or M204 would help control acceleration on the fly. Not sure why they'd want to change max speed on the fly rather than just use feed rates?
As for variable jerk/instant speed on the fly I'm not sure there is a way to deal with this with the current gcode library?
As there are already slicers in the wild using these gcodes badly perhaps it may be easier to have new gcodes for use in config files that can't be overriden in build files?
Edit: Whats the market share of Duet equipped/reprapfirmware compatible machines like vs Prusa compatible systems now?