The fact it theoretically exists doesn't make its existence useful or even sensible.

It might break code; but we really need to identify whether that code IS ALREADY BROKEN. I would give a 75% odds that any code using that pattern is actually broken already, and I give exactly zero cares if we break already broken code in service of correcting the single biggest gaping hole at the heart of D.

I would also put a ~60-80% wager on any real-world instance of that pattern already being some kind of move constructor, which will only benefit from this change...

I would put maybe 90%+ odds on any given instance of this declaration being written by a D amateur, who actually didn't understand what they were writing, and possibly thought it does something that it doesn't actually do; that is, I would wager with almost 100% probability, that if this exists in the wild, it's essentially an accident. (probably a failed attempt at a move constructor)

There is NO CONCEIVABLE USE for this pattern as it is today, outside a weird syntactic hack with some very weird calling semantics... so; we need case studies to consider.

We're just going to break this code, and you're just going to have to come good with that. I will personally submit a PR to every single repo affected by this change.