What status effects or mechanics would you like to see?

[Garlyle]

but nobody is really concerned what any of the values they have for these properties they have. All that matters are your core attributes, your rotation and dodging.

Well, Stun or Sleep resistance are actually pretty highly valued in PvP. That aside, the major difficulty in designing content around these things is the choice you end up on:
1. The use of ailments/elements isn't so deadly as to require these things, in which case people ignore them.
2. The use of ailment/elemental resistance becomes necessary to handle a fight - in which case, classes without the proper tools can't participate, players that haven't farmed up a bunch of x gear can't participate/get complained at because they're ill equipped for the fight, etc; creating content that an even smaller segment of the playerbase has the gear to actually tackle.

2 is a valid route of design, but XIV is probably not going to take that route, not without a significant set of changes.

[NovaUltimatum]

Well, Stun or Sleep resistance are actually pretty highly valued in PvP. That aside, the major difficulty in designing content around these things is the choice you end up on:
1. The use of ailments/elements isn't so deadly as to require these things, in which case people ignore them.
2. The use of ailment/elemental resistance becomes necessary to handle a fight - in which case, classes without the proper tools can't participate, players that haven't farmed up a bunch of x gear can't participate/get complained at because they're ill equipped for the fight, etc; creating content that an even smaller segment of the playerbase has the gear to actually tackle.

2 is a valid route of design, but XIV is probably not going to take that route, not without a significant set of changes.

Good point about PvP, I forgot it's useful there. My post is directed purely at PvE in that case. We already have useful mechanics available on some but not all jobs though (i.e. silence/stuns that can interrupt mob mechanics).

As for requiring them, you just need to make sure that the scaling is done right so there's a noticeable help with having attribute/elemental gear than not focusing on it at all. Parties should still be able to clear content without them, they just can't make use of the enemy weakness as much.