Now, if they ever do remake FF7, one thing that must be done imo is to shorten the Supernova sequence. That Safer Sephiroth battle can get so frustratingly boring if you don't kill him quickly enough. Though I realize that to many people, that would be low priority.
When it comes to a remake, I would not imagine that the dialogue, or at least the style of the dialogue, will be very faithful to the original. It seems a little out of Sephiroth's character to laugh evilly, which he did a little too much in the original FF7. What I imagine they'll do is simply have him smile instead or alternatively change his attitude to make him appear more contemptuous and loathing. They're also likely to tone down Barret's and Cid's dialogue, as although you can easily censor swear words when they're written down, it's not the same when there's voice acting.
Certainly, if they do create a voiceover for FF7, I'm praying that they take out Heidegger's "stupid horse laugh" (as Rufus calls it) and Scarlet's signature laugh as well as Palmer getting the hiccups while laughing during battle, because really, what kind of voice actor could imitate that in a way that doesn't sound ridiculous? Nevertheless, I'd be interested in seeing what kind of voice actors they get. I'd also be interested in hearing spoken dialogue from Bugenhagen and, more than anyone else, Jenova.
The worst thing they could do with a remake is incorporating a FF7AC-like battle style. Simply because that just wouldn't look right in many battles (the boss battle against Palmer comes to mind).