I would probably expect it to take effect over weeks and months rather than instantly.

I've got several weeks coming up with 4 hours of train travel every day, so I feel I'll have a pretty good idea by the end of that!

It'll have about as much success as the law that says no cycling on pavements.

Who's going to enforce it? People who play their slop videos and music out loud on public transport aren't the most considerate people to start with. They're not going to care.

I don’t think it will ever actually be enforced, so there needs to be an allowance for citizen justice instead.

It seems broadly decent to me. My biggest disagreement is that the penalty is a fine, because the severity of that scales inversely with how much you can afford the fine, but I'm not sure what a suitable alternative would be

While there is certainly going to be an issue of patchy enforcement like the utterly charming experience it seems like you're having, I think that's an unfortunate but necessary consequence of not requiring drivers be the ones to confront passengers. For the sake of them being able to safely focus on their actual job, some dickheads will continue being dickheads unobstructed, but less of that is still an improvement. The guidance does suggest that the driver is indeed subject to this as well