While I do not think that attunements should make a return in the form they previously
had, I do think that some form of them should return.
For example: Before entering LFR, you must have either done this quest chain, or have
done the raid on another character. (Downing the boss or doing the quest chain unlocks
it account-wide. Also could just be for fun overall, or required for all difficulties.)
The quest chain would not require previous raids or things from them, instead it could
require things from around certain zones, or the most recently added dungeons. The
chain would be able to be completed on multiple characters, but it wouldn't be required.
-IE: Past the first time, it's just for funsies.
(PS: I do in fact use LFR.)