Interesting ideas. I put in a request elsewhere corresponding to your first paraphonic idea-- that only those oscillators that are activated (running through a filter) would be triggered in paraphonic mode, so you could do just 1 and 2, or 1 and 3, etc.
The idea of using paraphonic mode to get two-voice polyphony is basically what you get in Duo/Split mode, although you have to play them on different parts of the keyboard. I'm not sure if your idea is technically feasible, but it's intriguing.
I also like the idea of Duo/Split mode being able to have two oscillators working paraphonically through one filter and one oscillator mono through the other filter. You can kinda fake this in Paraphonic mode currently by running Oscs 1 and 2 (for example) through Filter 1, holding two-note chords, and playing a solo part with Osc 3 (non-legato so as not to re-trigger Osc 1), potentially running through Filter 2. Your idea would make this quite a bit more elegant, but again, I'm not sure whether it can be implemented. I'd be curious to hear from the Arturia folks about this.