Up to me there are 2 main problems:
1) The infinite queue time due to the PvP rank sync
2) The WD, atleast up to me, is the real and the only PvP content in FF, and it could discourage people that like pvp and think they are not so good with it
(also sometimes you also find the "pro-player" that say "with that healer we won't be able to win", "It's all a xxx fault")


Sometimes I tried to check both FL and WD duty via Duty finder, but it totally wreck my waiting time.

The 1st problem is probably the most important one and they can do a lot for fix it, like multiple matches once you started (so you can even change strategy with your party once you lost), pvp roulette (let's see how they implment it), some kind of new little reward, like 5 allied seals, if you queue solo and win (to avoid trade party for bonuses), make a lv50 synced instance that will pop trying to fixing ranks, but will anyway pop(with only a solo/duo queue)...
The most alarming thing for me up to now is how they will implement the Duty Roulette, I highly hope that SE will give you the daily bonus reward only if in the WD you win or in the Frontline you achieve the 1st or the 2nd place, maybe allowing for doth the content to join in couple, in order to avoid pro-zerg and still let you play with a friend.
Giving the bonus only for a win up to me will incentive players to do their best and not just standstill, also if you lose you probably will redo the DR in order to get the daily reward, and this will help queue time again!

For the 2nd problem I would like to see a 8vs8 WD too, so helaers can hope in a allied heal, more coordination and strategies could be done and you can have more different roles in your party.
As Frontline is played even by players that don't like PvP so much, I think this will be a little incentive for those players.