Moving will be made to interrupt spellcasting at a point in time...

[Estellios]

This guy gets it! +1

(kindof not related but applicable)
From a tank perspective, I need to be aware of my healer's situation... so I see an eruption under my healers feet, I pop my "ocrap" rotation and self heal my way through it. That's right, it makes the tank's job harder, but I'm up for a challenge.

This is really how you have to go about it, the tank has to help the healers out too. You have more than enough time to Resonance > Cura and run back if you've ran from an Eruption even if your tank doesn't save sentinel for Eruptions on mages. Hell you usually don't even need Resonance and have enough time to get within normal casting distance. I've been practicing by standing still for Ifrit now whenever I cast and have had absolutely no problems at all. If they can implement movement interrupting casting and make it work well most people would have much less issues staying alive in the fight.