Specifically, I'd be interested in using Pianoteq as an effect. You have already done all the work to model a piano but right now the only way to get a sound into that modeled environment is to play a piano note. Would there be a way to input an external sound, say from an FM synth, into the virtualized environment, and have the virtualized piano generate reverberations, induced harmonics etc as an effect?

The real world analogy would be something like placing a guitar amp inside a piano, or singing into a piano, while the pianist plays.

Of course I understand this feature would only be of interest to a handful of more experimental musicians and may not be worth implementing as a result, but I figure there's no harm in sharing the idea.