It would be great to have the option to blend the two mics/cabs in the IR block while retaining the same overall volume, e.g by introducing a mix & volume control.
You can adjust the level / PAN for each cab/mic etc., is this what you mean?
Increasing the level on one mic will also lead to an increase in total volume making it more difficult to judge the change in tone (louder will often sound better). It would be nice to have something like a Ratio control to blend different mics keeping the total volume constant.
A lot of IR loaders provide these kind of features.