I would like this also, though most VFDs have 2 analogue inputs, one which could be connected to a potentiometer which can increase or decrease the projects rpm just need to check the VFD manual and function settings.. Unfortunately feed rate hasn't got that option yet
Noticed your posts as a result of reviewing old feature requests.
Were you aware that F11 / F12 will allow you to use the MPG dial for Feed Rate & Spindle Speed respectively?
I haven't tried it on my machine but noticed it in earlier feature requests and confirmed it is documented.