One thing most (if not all) blink tanks in FFXI feared... AoE attacks/spells. We have those in abundance in XIV (Just look at World Of Darkness for example... all of the bosses in that spam AoE attacks/spells), which would make Utsusemi useless. NIN was never meant to be a tank in the first place in XI, only some found a way to use it to their advantage and the only way they could hold hate in XI, was due to their subjob being WAR. Without Provoke or any other hate generating capability, NIN didn't work well as a tank. Utsusemi was merely a 'get out of jail free' card, allowing them to survive til the tank got hate back.

To make NIN into a Tank for XIV, the whole class would need to be taken apart and recoded for a tank role... and with another tank coming in Heavensward, I don't think SE has the time to do such a overhaul (nor intent to do so).