The record for consecutive ODI hundreds is three matches. If Alastair Cook makes a hundred in the third ODI against Pakistan, he will join the company of Zaheer Abbas, Saeed Anwar, Herschelle Gibbs, and AB de Villiers.
That company is higher rated than him in the one day game, all of them being candidates for being some of the greatest ODI batsmen of all time. While only two of them played in the time of T20, I don't think there would have been any debate that all of them would have made good T20 players, but it's taken as an obvious truth that Alastair Cook won't.
Now, I'm not saying that Alastair Cook belongs in that company, he's got a long way to go to match any of those players, but like all of them he's adaptable enough to play in any format he wants to. The main problem people seem to have with his batting is that he doesn't have enough big shots to play successful T20 cricket. This ironically is one of the same reasons people said that he couldn't play ODI cricket, and look how wrong they were.
The bottom line in any format of cricket is that if you don't get out, you can score runs, and Cook is good at not getting out. He knows which shots he can score from, and has added new ones to his one day game, like his supreme sweeping so far in this series.
Another irony about Cook's form in the limited overs format is that in many ways it negates one of his biggest weaknesses. Even when he's playing well, he always has to be cautious outside off-stump as his technique can lead to a lot of balls being edged into the slips. However, in ODIs and T20s the slips are generally nowhere to be seen, which frees Cook up to slash with impunity.
I'm not saying that Cook will be a success in T20 cricket, there is always the chance that he will fail. But is England's T20 team so good, and opening partnership so brilliant that he shouldn't be considered? I don't think it is.