Honestly I think BLU is in a pretty good spot right now. It's got a wide range of utility, it's got a spell that lets you solo dungeons now, lots of good stuff. I'd say it could perhaps use a few more tank skills since you are still pretty squishy even with a tank build.

Perhaps they could/should add more long term incentives to keep people playing BLU for longer, but otherwise I got no complaints about it. And it's not like BLU content is 100% dead, you can generally get a couple people in PF to run dungeons to get spells.