I think when ideas like this have been discussed in the past, we've tended to try to identify if the ideas could be adopted post 1.0 -- that is, are they compatible with the current Drop system. The principle being that we could have a smooth transition where we deprecate the Drop trait and transition to a new system like this one.
As far as I can tell, the proposal here falls into that category (since @arielb1 has stated that Drop remains solely for backwards-compatibility).