Is it possible to change the 7 day payout on steemit? What would be the obstacles to do so?

One of the obstacles is that it would allow users to vote many times on the same post with the same Steem Power.

Currently there is a seven day payout system which meshes with the seven day delay on returning delegated SP. If payouts were set for longer periods, or repeating periods, then it would be possible to use delegation to upvote a post many times using the same SP.

This could be achieved by delegating the SP to a new account each week. The new account would then be free to upvote a large number of the author's old posts before returning the SP to the user (with a seven day delay), with the process repeating on a weekly basis.

This reduces the "proof of brain" required to earn new SP.

(As a note, I believe that the old system with a longer payout period operated prior to the development of the delegation system).