If they basically continue the same story/quest formulas. Like, I was really pleased with how they incoming spoiler
let us play as Alphinaud in the latest patch
Which I found was surprisingly new for them to do. I expected it "if this was a regular game and not an MMO, X would totally be happening right now /begrudges the fact that FFXIV is an MMO for 3 seconds... then sparkles at the surprise/." I would like to continue to see "new" approaches like that. I was also pleased to see we got to make more choices in SB, and little things like our classes were acknowledged by NPCs.
Otherwise, it seems like SE is getting cosy how things are currently done because it's been successful up to a point and I think if it was the same gimmicks every time, I'd grow tired of it and quit. It's kinda like an artist drawing the same things the same way without ever improving themselves because they know X is received well (in general), so they get content and hit a plateau. However, I can tell that SE is trying to explore/experiment a little at a time while playing it safe, so I'm okay with that.
Other things that would drive me crazy: bad directing, IC inconsistency (I find Thancred a bit inconsistent between ARR and HW+, and Yda also fell out of character in HW [you could call it char development, but I found it really... poor in general]), no fulfilling sidequests to serve as relief from tragic MSQ, so many deaths so little time (at this point I just don't care if a character dies).
Start rant/ramble xD: and this wasn't enough to make me quit, but I really dislike the lack of variation in accents among the characters now. Like, in ARR (while fantasy/pseudo accents(I think)), Raubahn, Seedseer, Merlwyb, Alphinaud, etc., all had different accents and speech patterns from each other and I kind of imagined it to be a cultural thing. Now, the main cast has roughly the same or too-similar accents, and almost everyone has same/similar speech patterns regardless of character or origin (e.g. everyone says "you and yours" at some point, and while it's to display antiquity, it's a bit tiring. The same thing can be said various ways, you know?). It just really annoyed me that we went from a potluck of various fantasy accents to all UK accents from ARR to HW. Like, I get Ishgard being primarily UK accents, but Ul'dah, Ala Mhigo, and Gridania should have different accents, you know? I was relieved that Hien and other Doma characters did have slightly different accents (despite similar speech patterns and UK accent under tones) to reflect their different culture/area.
Edit: I totally prefer Raubahn's current VA over the ARR one (the ARR one, at least in the very beginning, was terrible), so, it wasn't all bad.
Edit 2: someone made a really good point: if the prices go up, I won't be able to afford it. Or rather, I won't want to afford it. My gym membership is cheaper (at $10 a month with contract), which you'd expect it to not be in this day and age... I'd rather save up sub money for more solo games if prices went up. I probably wouldn't go to another MMO as I tried 'em and didn't like 'em as much as I like this one.