Please add a way to do original content synced, specially missions from the original expansions and Champaign. Currently, thanks to the level sync status the battlefield imposes (without syncing at all), there is no way for the players to deliberately sync with each other if the way to (say, synchronize everyone's level to the lowest of the group).
Give players the option to do all the old missions synchronized if they so want to, please. It's really a no brainer function and even FFXIV gets it right.
Plenty of people I know would love to do old content synchronized and help new players do it for the very first time in a non steamrollable trivialized way (having some actual fun and challenge).
So, at the very least, remove the level synchronization buff effect when inside mission battlegrounds, or better yet: give players the option (and maybe some extra rewards for everyone, even job points for lvl99 players, etc.) to do old content properly synchronized to the original intended level (maybe even with the option to do it at the minimum required level and the recommended level).
Giving the players options is ALWAYS a good thing.