Plus it's not like NIN was the only evasion tank in XI - a well geared DNC could do it surprisingly well (or even PUP).
I'd much rather see Mystic Knight or "Rune Fencer" make its way into XIV over DRK as a new tank - DRK should be more offense oriented and take advantage of the great DD tools MRD has access to. Besides it's not like every job is locked into the same general role as the base class (see: SMN vs SCH).
That said, it's also one of the reasons I actually much prefer XI's design over XIV's when it comes to jobs, equipment and abilities (minus auto-learning stuff like spells I mean) - while outdated and flawed, XI's system was also infinitely more flexible than the armory system. You will *never* see BLU in this game because of it, it just can't work. BST won't happen either due to the nature of the game's content and how trashy most mobs are anyway (unless it was all based on Call Beast and no charm)