In example, you fight your way through hordes of demons with "Cleave", then from experience you know there's about to be an impending boss fight so you swap out your "Cleave" for "Frenzy", take care of the boss, then back to "Cleave".
This allows the player to have any skill they want within 15 seconds, as long as the skill they're swapping out isn't on cooldown. Personally, I feel this grants way too much freedom in the choices you have to make in Diablo. I think there should be some permanence when it comes to skill swapping, so I offer this alternative.
New Skill Changing System:
-You can only swap skills in town.
-There is a 5 minute cooldown between skill swaps.
-You will press "Save" to trigger your skills being swapped out and initiating the cooldown timer.
-There will be an area that you can enter, containing dummies and granting you the ability to swap skills freely. (For testing)
-When you leave the testing area, all of the cooldowns will still have been ticking down according to their original clocks and you will still have your skills that you had prior to entering the test zone.
I believe this will add a slight challenge to this game and will offer players the possibility of remorse. Albeit a bad feeling, players like myself enjoy the lingering possibility of feeling it.
Feel free to +1 if you agree with this and of course -1 if you disagree.