The ability to create a version of a 'testing' package to run on 'stable'.
There will be exceptions, but most packages should be able to have a script to create a viable back port.
There are good reasons to run stable - and good reasons to pull in newer packages. But the current situation is not really workable.
This will probably entail having a second set of libs and there will always be situations the are just broken, but the brick wall for the typical user wanting to pull in a package without mucking things up could be greatly improved.