I'm a fan of keeping flash in the game as a summoner spell, with a blink dagger-esque effect.
I feel that 3+ seconds of no damage taken would be a good amount of time.
It has been clearly stated that flash's initial intended purpose was initiation, so make it better for that purpose. If people continue to use it to escape just begin raising the time you must go without being hit. (Also, either A: Buff the hell out of the range, or B: Buff both range and lower cooldown)
On the topic of cleanse:
Cleanse is already a good spell by itself. Buffing it further will turn it into the new flash, no question. We don't want to replace one must have spell for another.
On the topic of a blink item:
I don't think that will fit well into the LoL metagame. In DotA skills do not scale with items, so you don't need to worry about buffing them. This is why you can simply buy a blink dagger and still put out good amounts of damage. If you have to buy an item here it will cost you in either general survivability or damage output, to the point where you wouldn't be useful.
On the topic of 'dash':
I think this is a cool idea, but I don't think it should be the same thing as flash.
If flash's range was buffed back up it would make a great initiation skill again, as it was meant to be. As it stands the range is so short you really can't initiate as well as you should be able to.
If you want to make flash a blatantly non-escape spell, make the duration you have to go without taking damage higher, such as 5+ seconds, then add 'dash' as the escaping equivalent.
More summoner spells that serve a different purpose is good.