Currently, the feedrate slider controls G0 and G1 feedrate override, simultaeneously. the suggestion is to split it into two, seperate sliders, and allow them to be hooked up in HAL.
To do this, means bringing the feedrate override through HAL, so is non-trivial. It also means writing a slider widget for the HAL VCPs. It is unlikely that the two slider option would be back-ported to the old style control panels.
A quick example of where seperate feedrate override is handy.
1) setups. You are happy with the cutting speeds (infact, you dont really want to cut slower, due to chip size, cutter wear etc) but at full G0 speeds, it doesnt give you time to hit a estop button if the machine heads off towards the part fixture during a G0 ... the ability to slwo down the G0 during the setup pahse would be handy.
2) CNC laser, waterjet or plasma. Feedrate override is often used to adjust the cut speed during the cut for minimum dross on the back of the part. Perhaps, you end up at 20% of the programmed feedrate .. this makes your G0 moves extremely, and needlessly, slow. Here, slowing the cut/G1 speed, while leaving the G0 speed as fast as possible is what the user wants.
The proposal is to have feedrate override into the motion as a pair of HAL pins, F0 and F1. F0 controlling the scale of the G0 speed, F1 controlling the G1/2/3 speeds. For the current emc functionality, F0 and F1 would be tied together and connected to a single slider output. For other modes, say two sliders, they could be split to two seperate sliders, or G0 connected to a fixed reference to leave G0 always "fast".
The above will need HAL VCP sliders implementing, and some thinking about how the old feedrate overide can be handled.