Is your feature request related to a problem? Please describe.
It is not related to a problem or flaw as far as I can tell.

Describe the solution you'd like
I would like to have specified in a character's TMW bar a condition or warning related to the specified spell to interrupt.
As in the Paladin Rebuke.
Sometimes in the heat of a fight you don't see the NPC's pending action, the spell being cast. So you might miss the interrupt chance.
Example, in Torghast, the Empowered Mage type casts a heal spell on itself that is interruptible. But if you don't the fight gets prolonged ad nauseum.
Another example is the Fear spell some cast that can be interrupted.

Describe alternatives you've considered
Nothing really other than having to watch what is being cast, seeing it in time, but then not watching other stuff which can be a problem. Especially if there are more than that NPC in the fight.
I did try to add in the Paladin's Rebuke to watch for the spell and make a sound. It hasn't worked.

Additional context

You can already do this with a Combat Event icon (to detect casts from any enemy) or a simple Spell Cast icon (to track casts from specific units).