A few small things
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MM/sec
current layer height/total layers
current travel speed(live update mm/per sec instead of speed of percent of something you entered 10 hours ago on a long print)
current print speed(same)
current acceleration settings
extruder retratction settings (live update) Hard I know cause this is done in the slicing software but maybe could be done in firmware
Serial console of gcode that is being transmitted. -
I'm not sure exactly what you mean, but here goes:
MM/sec: in what context? In GCode, mm/min are always used, probably because GCode was originally designed for CNC machines which use lower speeds than we do.
current travel speed(live update mm/per sec instead of speed of percent of something you entered 10 hours ago on a long print)
current print speed(same)The speed of the current move could be displayed, but how useful is that?
current acceleration settings You can use M201 and M204 without parameters to report them
extruder retratction settings (live update) Hard I know cause this is done in the slicing software but maybe could be done in firmware As you say, hard, but not impossible. Why not use firmware retraction instead?
Serial console of gcode that is being transmitted You can get this sent to the USB port if you send M111 S1 P3.