I'm going to reference a game that is not FFXIV. Though it's something I would like to see because it's really awesome, and as far as I know, no other game has done it, correct me if I'm wrong(except one).

Basically I want them to add an nm where it takes people from every server to beat it, collectively.
I don't really see anything new here. You're just introducing cross-shard PvE. Servers can barely handle all players gathered together at a set location, so I don't really see how that would work with all servers at once...

Similar things already existed in others MMO, it wasn't exactly cross-shard, but cross-faction. In DAoC, players from the 3 factions could gather in a PvPvE area (Abyss). Deep inside there was some huge monster (Legion). At first, because everyone's gear sucked, we made attempts with all 3 factions (no way to disable PvP, so we tried to be fair and not to kill each others) in order to defeat that NM. Results? We crashed the damn server.

Don't even expect that to change at 2.0. No MMO on the market is able to manage thousands of players fighting at the same location.