New Quests
MSQ is centered on Doma this time. New Hildibrand quests, but those are permanently getting moved to the .x5 series of patches. The Ananta are getting their Beast Tribe Quests, and they are a battle tribe.
New Dungeons/Trials/Raids
The 4-mans are Hell's Lid and The Fractal Continuum (Hard)! The 4.x series of trials is the Four Lords (yes, the ones on the map around Hingashi). The first one is Byakko, the white tiger. As for raids, we are getting Omega: Sigmasape.
Jobs/Relics
Jobs are getting adjusted. BLM's DPS and WAR's usability were mentioned, but there's a lot more then that coming. As far as relics go... The Forbidden Land of Eureka - Anemos is planing on being released in 4.25. Yeah... planed... the more pessimistic people think we probably won't be getting it until 4.3 given that SE originally planned on releasing it in 4.15. But hey, at least we know it has both Relic Weapons and Relic Armor... *goes back to farming Zodiacs and Anima weapons*
PvP
New Feast map and lots of PvP system adjustments.
Glamour System Updates
There's a lot of bad translations/speculations going on about this here's what's been confirmed about this. Also, a lot of the limits on this will more then likely be removed as the dev team sees how much stress this puts/doesn't put on servers.
First up, the current glamour system is not going away. It is staying (for the foreseeable future anyway) and can be used like normal. The only major difference is that there is only one glamour prism that can be used for everything. So no more running out of Goldsmithing specific ones...
The new system (called the Glamour Commode) is probably best described as an expanded Armoire. Items that are to be used as glamour are registered in the Commode with glamour prisms and can not be used as equipment (you can take them out of the Commode and used them as normal items again). Those items can then be used in Glamour Ensembles (sets basically) that can be turned on/off (there is a system command for this!). Things like dyes can be used on specific ensembles so it's possible to use the same item with different dyes in different ensembles.
The one big kink in the system is how limited is some respects. Gear still can only show up on the jobs it's limited to (IE: no SMN gear on a BLM, no healer gear on a tank). The Commode can only hold 200 items total. Items that go in the Armoire can not go in the Commode, but can be accessed by the Commode and probably do not count towards the 200 item limit. There are currently only ten Ensembles available. Probably the most annoying limits are that the Commode can only be accessed in an inn and Ensambles can only be turned on in inns, cities, residential areas and the Ivory Chapel (once they're on, they stay on).
It should be noted that SE is hoping to change the system so that the Commode can be accessed outside inn room and presumably that Ensembles can be turned on where ever. It looks like once again, all of this will depend on server load. The same thing goes for the amount of items stored and the amount of Ensembles. But hey, at the least I have somewhere else besides my retainers to store 200 pieces of equips I specifically use for glamours and that makes me pretty happy.
Item Storage Changes
Speaking of more places to store items... items now stack to 999! And chocobos now have saddlebags! They can now store 70 items. And they can only store them. If you want to use them, you have to retrieve them from the chocobo first. And yes, you can retrieve the items from the chocobo while their stabled. From the looks of it, you're chocobo's location doesn't effect if you can get the items. It's pretty much an entire extra inventory bag for you. Hoarders/Crafters/Gatherers rejoice!
Duty Recorder
It is now possible to record instanced duties. This is not a recording of the visuals of the fight, but rather the packet information. There's a lot of constraints on this for various reasons (hardware, drama, etc.) so I won't go into it in detail.
Other Stuff
In addition to airship exploratory voyages, FCs now have submarine exploratory voyages. Perform has a new UI which looks like piano keys. Tomestones of Mendacity are added. The 8-man MSQ dungeons and Hidden Canals of Uznair are being adjusted. EXP gains for DoH from Lvl 50-60 is being adjusted.