I would definitely consider Haiku for music if it had the same low latency capabilities as BeOS, but latency aside, a lot changed since the BeOS era: today pretty much all non consumer audio interfaces are external, therefore driver support for them is needed as well. Also it's not uncommon to see hybrid systems in which Linux runs a DAW and its plugins under WINE. It's a mess to configure and breaks very easily (lesson learned: don't do that in your tinkering machine that you upgrade often or install/compile different kernels etc. use a separate machine for Linux+music), so a WINE port would be useful as well, but I guess it'd be a huge job.