Necro-posting because this has a core idea of wider interest. We were discussing adding a realtime postprocessing effect to VA's text-to-speech output, for theatrical effects, such as octave shift, robot voice, and more advanced effects like a Granulator are feasible using freeware.
Facerig is not actually the best solution, I just mentioned that it can do ie robot vocoder effect in realtime - as can some apps aimed at videochat or livestreaming, but if you're not using the furry 3d animated avatar then you're taxing your graphics card for no reason when it's already busy - and they have some commercial licensing restrictions that could possibly affect you.
We actually want a lightweight app that just takes a selected Windows Audio Device as input and applies one or more VSTs of your choice to it and pipes it to a selected Windows Audio Out device, real or actual, with the shortest delay possible and least overheads.
I think "VST" is the magic word to research on, it's an old plugin standard for live audio processing and there are a lot of options and a million free filters to choose from.
Maybe an engineer or programmer can suggest something barebones that would suit streaming, I do not have a go-to version of this on Windows. But Facerig can absolutely do it, as one option that I've tested.
It would also be possible for Gary to go down to his shed and bang VST support into VA, in theory :p