I think 40 was an arbitrary number to contrast with 400. Don’t focus on the number. I agree with your definition of immediate but I think that such a solution would have to allow a slightly broader definition. I can easily think of relatives who would be in a fury to not “be allowed” at their favorite uncle or favorite cousin’s wedding.
I think that cherrybim raises a very excellent point. It is easy to say that takanos don’t work because rabbonim and rich people don’t stand behind them. But there is also the aspect of not wanting to cross paths with the mechutanim. Which is exactly why only a lo plug could work.
I truly believe that it would be a very beneficial thing for the askanim and rabbinical leaders of our generation to enact. I hope that they will decide to do so. This is a tzora gedolah for klal yisrael, right up there with tuition (not trying to be funny).
The prevalent argument “It’s the most special day of their life, make it memorable” just doesn’t fly. It should be a special day with or without pomp and ceremony (above what halacha calls for) or we have raised a generation with bad values. It has always been the case that rich people had nicer chasunas (that all the town beggars looked forward to) but apparently that didn’t cause a spillover problem as it does now. So it is still dependent on the wealthy to “take a hit” in this case for the sake of the greater good – the tzibbur.