I think Lost Island HM has the exact level of difficulty, that beating it requires both decent gear and skills from all the players, and yet it's not too hard that it becomes an "elites only" Flashpoint.
Speaking from experience as a tank, the first time I encountered the first boss, I was slightly undergeared (missing 2 Columi pieces), and I totally panicked. But after a couple of runs (5), we picked up the rhythm, and we finally beat the boss. The process might be long and painful, but in the end it was fun and rewarding, because it required more teamwork than before, and what's MMO without teamwork?
Now after having beaten LI HM a couple of times, it's still fun, because even now I have better gear, you still need the concentration and the cooperation from the players in order to succeed. You can allow yourself one or two mistakes, which is great, but screwing up a bit too much will still cost you, even if the whole team is on Rakata gear. For me it's the only challenging Flashpoint in the game, and no, I do not want Bioware to nerf it, because then the whole game will be a joke, if every content in every mode can be lead by a undergeared/skilled tank who has one of his eyes closed during Boss fight.