sounds perfect to me, more than i'd have needed, still easy and full powered!
just add a "boost" page in the rig menu with a few parameters:
pre-gain boost
post-gain boost
delay mix
(delay feedback)
reverb mix
(reverb feedback)
realtive values should work best ( + 5 % instead of 30 % fixed)
since in the rig menu this would have to be done for every rig, but maybe you could (must!) be able to set some defaults globally.
i perfectly see that this will be some lines of code to be written, but as i think it's gonna be a new and smart killer feature to be well respected by most users...
edit: to answer the question ck, i'm pretty sure that by the solo-boost request we're talking about is a simple volume bump.
this would do the trick for me easily, but as we're looking for smart solutions here, this superboost might be a go to feature...