A great feature for me would be a new EQ block with resonant filters.
This (bump at the rolloff frequency) makes it easy to simulate the EQ response of a cabinet (without some of the muffling resulting from “miked cab” IRs), similar to what OmniCabSim or Broughton RFE pedals achieve:
It would basically have with 3 EQ points, 2 or 3 parameters each:
1- HPF filter with fixed -12db slope: frequency sweep and +/-10db gain/cut at rolloff frequency
2- LPF filter with fixed -12db slope: frequency sweep and +/-10db gain/cut at rolloff frequency
3- Mid Parametric gain/boost: frequency sweep, +/-10db gain/cut and bandwidth (Q)
This can be done with existing EQ blocks but needs a lot of tinkering. Just sweeping HPF/LPFs to change the response to replicate smaller or larger cabs, and adjust to the room in a pinch, would be very practical and effective.