Have I unlocked all the game mechanics?

[Eltaire]

Some of the later high level (post level 50) content requires that you have completed the story to unlock, so it's recommended to do all the main scenario quests to enable you to continue with, and unlock "Chronicles of a New Era" quests which are actually quite fun.

[Garlyle]

Some of the later high level (post level 50) content requires that you have completed the story to unlock, so it's recommended to do all the main scenario quests to enable you to continue with, and unlock "Chronicles of a New Era" quests which are actually quite fun.

Basically everything that's "level 50" content requires the completion of the Main Story, actually - I think Wanderer's Palace might be the only thing level 50 content that doesn't require completion of the 'final dungeon' that is Praetorium.

As mentioned, there are lots of mechanics you've still yet to unlock, some of which will also be tied behind story progression.

[Kloe]

As some people have said to describe FFXIV, the game doesn't start until you're lvl 50 and have completed the 2.0 main story quests. Obviously there are things you can do without being lvl 50 and not having the main story quests done, but you're severely limiting yourself in what you can do and will most likely get bored with the game and quit eventually.