What I'd like to see in any regen-capable controller is an ebrake input that can take a linear sensor. Maybe some even have that; I'm going to test it with the Fusin I have here as soon as a spare throttle sent by Ianmcnally2 (plus some other stuff) arrives (between times of checking on Hachi).
Basically the operation should be that if you use a standard ebrake lever with just on/off switches, it'd just turn regen on or off. But if you use a linear hall sensor as the ebrake input, it'd use that linear signal to control the amount of braking.
In theory this only requires a software change to *any* programmable controller, but it would require whoever wrote the software for the controller to make the change and then to make the update file available to everyone. Not a likely thing to happen.
Except maybe for Keywin / Ecrazyman controllers, as he seems willing to do a lot of stuff to advance the state of technology.
Of course, the controllers are probably designed with input logic that does not read the analog level of the brake line, but only whether it is above or below a certain threshold level, as a simple on/off input. In those cases, there is little likelihood of making regen work the way we'd like in such a simple method as just changing the device it's input with.
However, even with those controllers, if the MCU they use happens to be programmable for what it's inputs do, such as using ADC's as binary inputs, *and* that's how the designers did it for the brake, then in theory (assuming no input filtering logic/etc. outside the MCU between it and the brake input) it is still just a software change, simply a more radical one.