Just my 6 cents to mention after watching these vids:
1) I just hope that every job has versatility and utility in general. By versatility, i mean that there is more than just 1 way to play a job. Even in group settings i would like to see some kind of moderate flexibility in how you can play. WoW managed to overkill this with skill trees and XI did it with sub jobs. Of course in XI, there were only so many viable SJ's to use with a job and the variations were marginal at best. I dont know the best way to incorporate this feature without diluting or overlapping skills with other jobs to the point where everyone is a swiss army knife.
2) And by Utility, i would hope that every job has a unique function about them in battle aside from the melee DD, range DD, or heal function that they're assigned to. Kind of like how thief had SATA and treasure hunter or like how red mage had a unique support role. It seems like they're doing this so far.
3) if the battle system is going to favor a faster pace, i am a little worried that i wont know or see what my team is doing. The best part about XI's pace was that i could see the entire party's actions, while being able to communicate TP% for skill chains and other coordinated attacks. I really hope there is some kind of combo system, whether individual, team based, or both so that it keeps battle engaging. WoW was really lacking in that department, it was more twitch reaction (ex: sheep the skull icon, trap the X icon, or kite the diamond icon) and then spam dps after. But at the same time, it would be nice if the party could move a bit, unlike the camp > pull > kill > rest cycle that XI had.
4) As for scaling mob difficulty and instancing, i hope they keep it similar to XI where there were parts where you had to pay attention to where you're exploring or else get killed by something horrific (elementals, gobs, giants, etc). but at the same time, have solo friendly areas where mobs are easy to a moderate fight. I know they want to keep the game more solo friendly than XI, i just hope they find the right balance for this. In WoW this only mattered when you were instanced and fighting elites, or if an opposing faction was harassing your side of the world.
5) For Instancing, hopefully it will not be overdone like they did in WoW. I want the journey to becoming max level to be both challenging and rewarding at each phase of each job like they did in XI. In WoW, everyone can basically get a max level everything with top tier gear by grinding instances and raids. I would like to see more pride in the job you decide to take on, this worked well in XI. Lastly, I would like to see some kind of function for a zone other than grinding quests. In other words i want beginning zones to still matter even after you outgrow it. Pulling was an art in XI, and i hope they can keep some of that style intact in light of the faster pace. Too many instances will make the open world a disconnected place to the point where nobody will care to explore it anymore.
6) What made XI my favorite MMO ever was the social aspect. This was something sorely missed in WoW, because in WoW you could be very independent and everyone was competitive & aggressive with each other. I would like some kind of community collaboration and demand for helpful types of players. The best thing i can give as an example is the WHM in Jeuno who you always knew gave teleports for cheap or the random whm nearby who would offer a raise. WHM, RDM, and BRD were probably everyone's best friend in XI for party settings, but also a b**ch to find at times. I hope there's a way to incorporate this without feeling like they're as rare as diamonds.