I remember making my opinions on FF in several of your A-H related threads, Cali, so I'm not going to repeat myself too much.
I mostly want to point out that FF does not have a good chance of living for very long after he succeeds FJ- Hell, FJ might outlive him anyways like OTL. No, not because angry Magyars assassinate him or something. Franz Ferdinand had tuberculosis since the early 1900s- it was enough to make people believe that he would renounce his rights to the throne. Of course, that's not the point of the question, but it's a tidbit that is always forgotten about the man despite how well-known his poor health was at the time.
Rergardless of my notoriously negative opinion on FF, it's actually very hard to pinpoint exactly what he would do. Supposedly, he was pretty impulsive and changed his mind very often and contrary to popular belief, he never wanted to enact the US of Greater-Austria. At least, not in the way we know it. He definitely seemed to lean towards a form of Trialism to replace Dualism. Whether this was towards Croatia, Bohemia or all Slavs somehow, I have no idea. He was hellbent on reducing Hungary's status within the Empire, that's for sure. His hatred of the Magyars is more notorious than my hatred for him.
I'm honestly not sure how much the economy would be affected. Obviously, with no war, A-H's economic growth continues uninterrupted, though we can assune it'll slow down eventually. If FF manages to reel-in Hungary, then the latter's prosperity will undoubtedly be hit pretty hard and considering his neo-absolutist tendencies and desires to centralise, that can only spell bad things for the regional economies that strive thanks to the autonomy of the regions and the investment from the local governments.
Society-wise, the problems are much more obvious. Like I said, Franz Ferdinand was much more autocratic than his apologists make him to be. Since he also looked down upon the non-Germab ethnicities of the Empire, I don't think he had much to contribute to the Nationalities Question. At least, not much to mend the problems raised by it. In fact, I see him more likely to make thinfs worse. When FF replaces FJ, he will seriously need to address the issue since he can't continue to ignore it like FJ did. It'll just piss off the minorities, after all. Since he never really showed any interest in doing so other than blaming Hungarians and vowing to destroy their power, I doubt he would be able to do much good (if not make things much worse through his Magyarophobia and Germanophilia).
Speaking of Germanophilia, it's pretty clear that FF and Wilhelm II had a very good relationship, so the alliance isn't going anywhere with FF at the helm. He's going to need him when/if the Magyars (and likely many others) decide they've had enough.
Oh, I also recently read on the German wiki that Franz Ferdinand intended to take to reign as
Franz II (and not Franz Ferdinand I as I've seen so often here). Not too subtle about his absolutist tendencies there, Franzl.