Would people be willing to ditch the loudness (or have it work differently, possibly not correctly) in favour of bass and treble?

Yes. In fact, if we could also have some control over the slope and cutoff point of the loudness control, that would be ideal.

When playing with the RTA stuff, I noticed that the loundess control was only really affecting the deepest of the sub-bass frequencies. It had a very sharp frequency peak in the near-subsonic range, and not much above that. I'd rather have it more smoothly increase all the low frequencies instead of just the sub-bass.