Quote Originally Posted by CosmicKirby View Post
$20 that the new deep dungeon is going to be Heaven On High, the sealed giant Jenga tower in the Ruby Sea.

They haven't clarified what level Eureka content will be geared towards. Similar to how you could run FATEs on characters who WEREN'T max level in Heavensward, you might be able to level while doing Eureka Content. It hasn't been said yet.
He's talked in more recent interviews how he's planning for Eureka to be the means of expanding your character beyond 70. Among the content involved will likely include relics, but they are being moved into something on the side, rather than being the thing to progress with like before.