A bit of feedback before I get to voiceovers: the pacing of the content in this game is really good, at least for players who take their time and have not reached endgame. Unlocking the airship pass took many hours of playtime, and many more before I could join my Grand Company. The monster aggro that is subtly placed as a soft level barrier kept me from seeing everything the first week and then getting tired of it. The unlocks are sometimes easy to miss (sightseeing log) but other than that, XIV has been good at feeling like an open world sandbox, while gradually taking you through a tutorial.
I'm glad Heavensward is coming out next year, since my biggest worry was that I would run out of major content to do and end up with the same coil grind, tome capping, relic chasing garuda farming deal that everyone at endgame is stuck at.
So that's the positive feedback on the pacing.
One thing that would make it much more enjoyable for me is to have more voiceovers in cutscenes.
Some of these are done very well. The Grand Company rememberance ceremonies with Alphinaud, Alisaie, and the three GC leaders were some of the most immersive and memorable parts of FFXIV. Some other pivotal events in the main story quest however are shown with text only, or start out with voiced dialogue that suddenly cuts out after a few lines. The BGM also doesn't change. I don't expect voiceovers for every small fetch quest, but having one for the Ascians at the mansion would make sense.
Stories like that of Mylla, of how she came to be First Sword in the Gladiator's Guild, of Aldis and Leovol and their fall from fame - one of my favorite stories, would really have benefited from the full cinematic treatment like you see with the Iceheart intro.
My hope is that 3.0 will come with increased production values. Since most active players are up to 2.4 there is little benefit to redoing existing content, so I don't expect Square Enix to consider that at all.
More characters, more music and more story are what will keep me subscribed for a long time!