Simply put: What design and philosophy changes do you expect to happen going forward? I've been thinking about this a lot lately, and it's something I'd like to delve into as a topic of discussion.
Here are some of my ideas:
*Disclaimer: These are just speculations that I have mixed in with my opinion. Some of these topics have been discussed before and in far greater detail. I don't claim these ideas to be new or original.
Azeroth will be revamped in some way. Not sure if it'll be another Cataclysm type expansion, but I do think you will eventually see older zones get the Legion treatment where they match your current level to some extent. To elaborate: I don't think places like Westfall, the Barrens, and STV will be level 110+. I think they'll cap off at 60. Perhaps they'll continue the world quest formula where, depending on your level – you can do quests in older locations for decent rewards.
Model/world updating: This is something we're currently seeing in Legion. I think Blizzard is going to continue slowly updating models and the world that date back from Cataclysm until Vanilla. *I highly doubt you'll see any drastic changes to Outland, Northrend, etc.
Classes/races: Because of Legion's well received take on class fantasy/identity, I'd like it if they took it a step further and maybe even go more in depth on the races of Azeroth. Maybe they'll consider sub races since it has been something that players have been asking for a long time. Mag'har orcs, high elves merging back with the blood elves, etc.
Gear: I wouldn't be surprised if they kept the artifact system in place to some extent. Improving on the formula and giving players something to do at max level other than getting better gear, etc.
New races: Shot in the dark on this one but if we end up traveling to another world in an upcoming expansion I think Blizzard will introduce a new race for each faction that no one has seen before. Other than that, all I can think of right now *are ogres. Sorry, I'm not that creative.
New classes: Next one will probably be cloth/mail based that's non-melee.
Antagonist/Expansion: Maybe Azshara and N'zoth with an Old God themed expansion in the South Seas. I don't think Blizzard will go too much further into the *Burning Legion due to the "orc fatigue" that we've encountered in the past. Maybe put it on the back burner or eliminate them completely.
Sandbox MMO: At some point WoW may slowly deviate from theme park MMO's to a sandbox style MMO. Not overnight of course. This is the most out of left field speculation that I can think of.
tl;dr: Azeroth revamp, cloth/mail class, sub-races, new/unseen race, race identity, continuation of Legion successes, model/world updates, Old Gods, Azshara, the South Seas, larger world quest scaling beyond Legion to new and old content, and perhaps a sandbox MMO.
What are some of your ideas?
Edit: Removed sentence: "Mind you, if they don't change much from the earlier expansions."
Additional Edits: Spelling, grammar, and sentence structure (work in progress).