Does JACK even have enough information to do any-to-any latency compensation? The only "Linux audio" application that I know of that really does this now is Ardour, and it was only in the last few years that it was implemented.
That's the problem, the JACK design does not allow for it. It's why Ardour is still gimped and can't actually do full latency compensation if you connect a track to more than one sink, because Ardour is built on JACK, and JACK can't handle that, and the non-JACK backends for Ardour are kept at feature parity. (You can work around this with sends instead of connecting track outputs, since Ardour handles those outside of JACK)
JACK in general provides latency information throughout the chain, but it does not add delay lines to compensate latency itself, so the problem is that when you connect one thing to more than one other thing, the latency number becomes ambiguous (a range) and you can't compensate for it any more.
