i am suprized that haven't added delay to annie's ult

That's something I find curious as well. Veigar sees little play and can't blow up a whole team. Annie sees quite a bit and can blow up a whole team. Both had instant stuns, yet Veigar was the one that got nerfed. It's arguable that Annie has an indicator as to when she's about to stun. In practice, that little cloud of smoke is useless because you can just press E at the last second to get your last stack before instantly dropping Tibbers.

It will happen, I'm sure of it. We'll just have to wait.

Would they lower the cool down to non-ult levels?

They could increase the range of the ult making it a skillshot instead of being instant. So Annie can toss tibbers like in the video she was featured in.