Umm deep dungeon for new player perhaps current players can expect a glamour pieces to add their inventory perhaps.
They've already said we'll be able to work toward weapons with high iLevels through Deep Dungeons. That, alone, will keep that content popular.

As for Diadem, I don't want to speculate on what SE has planned. I'm eager to find out, though. Diadem seemed like it was envisioned as the FC-friendly battle content the game is currently lacking.

Hardcore endgamers will blow their fuses no matter what happens. SE shouldn't allow such a small portion of the playerbase to hold back development for everyone else.