My two cents on this...

I don't feel it's necessary, in all honesty. Don't get me wrong, I think it could have its benefits, but the problem is still a lack of attention. If you know a monster can cast a single-target doom, you're ready to cursna the hate target. If it's an AoE doom, you want to be ready to cursna bomb the tanks before the DDs (or the main DDs if they're the tanks, i.e. WAR etc). All melee fighting an AoE doom-using mob should have Holy Waters or be prepared to run in/out if they can't bother to take the time to prepare. And in the event that multiple people do end up getting cursed, a simple "doomed" should suffice.

Your biggest argument is that the chat log can get flooded in battle between people yelling doom and an alliance of people wailing on one mob. Two issues with this, in my opinion: 1) If you're fighting with an alliance and the majority of them get doomed without any way to remove it (holy waters or cursna if a mage happens to wander too close for god knows what reason) then that's just abysmal planning. 2) Chat filters. Why is the concept of chat filters so hard? People get doomed, they say doomed. Mages place priority order and remove curse as they can.

Even if a person's at 3 seconds it's worth giving it a shot as well, as I know I've been saved at 1-2 seconds more than once simply because I wasn't high on the priority list and had to get tossed a cursna later on. The mage order of operations in these situations is generally Cursna tanks > keep tank's HP up > Cursna others if tank is doing okay. Generally they'll try until a person hits the ground, and a simple typing of "doomed" or "doom" should suffice to say if you're still afflicted, with "clear" to state that they're good to go.

tl;dr - It'd be nice but it's not necessary by a long shot.