I wondered if there could be a new synthsis engine creted for ZynAddSbFX that'd focus solely on advanced fm synthesis.
What I mean is a multiple-operator synth with everything-to-everything modulation. I like how FM8 solves that with a very interesting modulation table that allows both self-modulation of operators, as well as forward and backward modulation (A can modulate B, and B can modulate A, while B can modulate itself also).
All the influences could be controlled by envelopes and LFOs as well as ghand-automated otr modulated live via MIDI CC.
I know this is a huge thing to pull off. But if someone is looking for a big new thing to code - here's an option :)
Using such a synthesis engine sounds like great fun to me, but zyn's main complaint is the complexity with the existing 3 engines. In my opinion this would make a good enough standalone synth on it's own given how tricky it can be to get heavily modulated soft synths right.
I don't know if it uses a full modulation matrix, but if you're looking for a modulation heavy synth which isn't aviailble yet I'd recommend watching out for 'Panther'. I think it's mid-alpha at the moment, but it certainly has some soild math and sounds involved already. Listen to some of the demos at https://soundcloud.com/wrl if you have a chance.
I just double checked with the dev and it has custom routing which is controlled via drag and drop.