I was looking through the list of bugs milestoned for 7.12 today and
stumbled across #4879. This ticket has been with us since 7.0.1 and
proposes support for the DEPRECATE pragma on exports. I seem to remember
seeing this feature being requested numerous times to help in dealing
with transitional issues in the core libraries.
If this is the case then we should aim to get this feature in to 7.12.
This shouldn't be a difficult task as there is a working patch  in
need of only a bit of minor refactoring already attached to the ticket.
What we need to make this happen is for someone to step up and write a
specification (on the GHC Wiki) defining the syntax and its semantics,
and then check that the patch faithfully implements that specification.