Cooldowns force the player to not use the same skill within an allotted amount of time. While conventional, I don't see the harm in attempting a variation on this system. My idea is simple, yet in my opinion, dynamic. My basic idea is having 2 separate cooldowns for a single ability. One cooldown is a "soft" cooldown and the other a "hard" cooldown. The hard cooldown acts exactly like cooldowns in most games, preventing the usage of an ability for a period of time, nothing new. The soft cooldown is my main focus. Basically, when you cast an ability, the soft cooldown begins after the hard cooldown ends. During the soft cooldown, an ability can be cast, but casting during this cooldown applies various (positive and/or negative) effects to the ability or yourself. For example:

Player 1 casts "Stasis" on Player 2.
Player 2 is lifted into the air and becomes immobile for 2 seconds.
Player 1 strikes player 2 with a sword.
Player 2 is released from "Stasis".
Player 1 casts "Stasis" on Player 2 during the soft cooldown. (+40% mana cost)
Player 2 is lifted into the air and becomes immobile for 1.6 seconds.
Player 1 strikes player 2 with a sword.
Player 2 is released from "Stasis".
Player 1 casts "Stasis" on Player 2 during the soft cooldown. (+80% mana cost)
Player 2 is lifted into the air and becomes immobile for 0.8 seconds.

In this example, Player 1 consumes considerably more mana by spamming his/her "Stasis" ability which could cost them the fight at the end. Let's look at another example displaying possible positive side effects for the user.

Player 1 casts "Fury", attack speed is boosted 50% for 10s.
Player 1 stabs Player 2 repeatedly.

Player 2 flees.
Player 1 casts "Fury" during the soft cooldown, attack speed is boosted 30% for 10s, movement speed is boosted 10% for 6s, Physical defense is reduced 20% for 15s.
Player 1 stabs Player 2.
Player 1 casts "Fury" during the soft cooldown, attack speed is boosted 10% for 10s, movement speed is boosted 15% for 6s, Physical defense is reduced 40% for 15s.
Player 1 defeats Player 2.

In this example, Player 1 manipulates "Fury" to boost his/her movement speed to catch the fleeing foe while risking his/her own safety. With some teamwork, Player 2 could lure Player 1 to allies where he/she would be susceptible to attack, especially once the movement speed boost wears off.

In conclusion, with this implemented, I feel that players will be given more choice during battle, resulting in more dynamic gameplay. A desperate player quickly putting up another magic barrier in hopes of escape at the cost of mana and movement speed, or needing to cast an offensive ability immiedietly in order to survive at the cost of attack speed. While I don't know what Zenimax has already implemented and if this idea could exist in TES:Online, I don't think it would hurt to post my idea. I hope you find it at least interesting.

It definitely sounds more interesting that the standard MMO "You have used a skill now wait x seconds to use it again"
I wouldn't mind it as part of the games system, though I am not a great guy for knowing what's balanced in PVP so others might see a flaw where I don't

Whether not it will fit in with TESO we'll have to wait and see, annoyingly we know very little about the games mechanics currently.