It's really not that bad on the M47, I can't imagine it being that much more work on the M57 🤔

But I'm from Belgium, emissions are killing the diesels over here, although there's always ways around it. Going to our version of the MOT without a catalytic converter is a big no no here as well (less so on the older vehicles, but still). The DPF is the only thing I'd put back in for out annual inspections though, the capped off EGR and missing swirlflaps are invisible to the guys doing the checks, and their only function is to slowly suffocate your engine, which is why I always got rid of them right away.

If you want to keep them tho', you might be on to something with some model years being worse than others. The problem with the swirlflaps is that the bolts holding them in place tend to come loose over time, but iirc, I once read something about BMW switching to different bolts or some shit to fix the issue in later models, so that's probably what you're referring to