What's going to happen is that where landlords decide to allow music its going to happen, and where they don't (or where they are instructed by their bosses in the chain), it won't. If there's a complaint (for example from a neighbouring pub) and the council decides to lean on the landlord, the landlord will give way.

So there won't be many actual court cases at all. The law matters insofar as it will have an impact on which way councils decide to jump, when some kind of complaint is lodged. And there is plenty of leeway fro them to interpret it either way, more especially since it won't in practice be tested in court except in very occasional cases. Which means it will be quite some time before any case law has built up.

In the meantime I suspect it won't feel very different from what it does now. But I'd hope there might be a few more places, pubs and non-pubs which will have got their heads round applying for a licence to cover live music.