Welcome to the community!
to take it to the next level, I would suggest implementing a linear phase option. This would limit the phase distortion introduced by each filter.
Note that using minimum-phase filters to shape a response doesn't necessarily introduce phase distortion - on the contrary, if you use a minimum-phase correction filter to 'fix' a minimum-phase frequency response peak you will actually fix both the magnitude and the phase errors. This is because a minimum-phase response error implies both a magnitude and phase deviation - so a complementary minimum-phase correction filter counteracts both.
On the other hand, using a linear-phase filter in this case would only correct the magnitude response error, while keeping the original phase response error untouched.
Many of the in-room low-frequency response resonances should be close to minimum-phase, so use of IIR minimum-phase filters makes sense to me in a general sense. EQ (including RoomFit) is anyway not well suited to fix non-minimum phase response deviations (e.g. nulls caused by SBIR or an out-of-phase subwoofer). Those should be resolved by other means (optimal placement, acoustical treatment, subwoofer integration, etc...).
On the other hand, having more options in RoomFit for advanced users wouldn't hurt, I guess!
Also, it would be nice, when performing roomfit on a limited frequency range, to be able to limit the number of eq filters. Right now all available filters are used regardless of how narrow the frequency range is.
This is a very good suggestion, IMHO!
It would also be great if RoomFit could automatically assign less filter bands, depending on the need. I fully agree that assigning all of the RoomFit PEQ bands in cases where most of them are doing minimal work doesn't make sense.
