As AU (and also VST3) plugins support sidechaining natively, I suggest to extend the send meta device in a way that all loaded AU plugins with sidechain functionality are selectable too!
I think it would be more complicated to support sidechaining for VST. And I don’t really know, Renoise does not support VST3, right?
AU sidechaining would be a good start, and maybe not too much effort to implement.
I think current combination of env follower + gain or follower + dynamics isn’t really the same because of limitations of the env follower.
VST 2.4 supports sidechaining, too, via 3+4 audio input for fx.
Are you talking about signal follower? What are the limitations? It may need some tweaking but works great, at least for me. I don’t use AU but i expect it to work like vst.
I would think you can use signal follower -> instrument automation -> AU / VST plugin combination, assuming that you can find your plugin FX alias in instrument list.
I tested this with classic compressor and reaXcomp vst plugins and only classic compressor was on alias list. My guess is that it’s because reaXcomp have sidechain build in and classic doesn’t, not that it’s needed with signal follower.
The signal follower is not very precise especially in lower/fast response areas, while AU compressor plugins that are especially designed for sidechaining usually have already the perfect and balanced response values inside. Also plugins can have different algorithms for level detection/calculation, so the character of a plugin will be also lost if using env follower.
A professional DAW has to have a sidechaining option, just as VST3 and AU provide it - that’s my opinion.