No idea whether it's "fast" idea, but:

- USE flags aliases

This could solve problems with USE flag name changes and breaking dependency 
tree because of it.
Placed, let's say in profiles/{use.aliases,use.local.aliases}

example - use.aliases: (no idea whether global aliases are really needed)
# <global_use_flag> - <alias1> <alias2> ...
xml - libxml2

example - use.local.aliases: (more real-world scenario)
# <local_use_flag> - <alias1> <alias2> ...
dev-libs/soprano:sesame2 - java
media-video/transcode:dvdread - dvd

-- 
regards
MM