Apparently I will never learn to only top-post when using discuss. Here is my reply to ezyang:
This proposal seems to be basically what I sketched out in that e-mail I sent out a long time ago (this is the same message that was linked from the original blog post):
https://mail.mozilla.org/pipermail/rust-dev/2011-December/001036.html
When I say “introduce incoherent traits”, this is basically what I am thinking of. Introducing the ability for traits to be declared where coherence doesn’t apply, but at the cost that the user must manage the impls more explicitly in the case of overlap.
As you say, though, I think this ship has sailed for the moment. We can come back and revisit this question later but right now is not the time to go mucking with the core trait system!