WotC said they plan to continue supporting all editions. Revoking the GSL would be hard to justify with that stated direction.
Is there anything to be gained by cancelling the license?
One thing they might well consider is to simply stop processing any of the book-keeping associated with the license - meaning no new licensees, no updates to contact information, etc - but leaving the license itself in place for current users.
(The alternative is to kill the license completely, which would probably affect very very few users, but affect them quite badly - and would probably lead to a PR hit far out of proportion with what's reasonable.)
If WotC stops processes unilaterally without updating the license then there can be more licensees -- the license goes into effect after the applicant sends in a Statement of Acceptance (SoA) unless WotC sends back a rejection.
They could roll the 4e GSL into whatever they are doing for 5e. Whether that be a new GSL or OGL or whatever. Since they have said they don't care what edition you play as long as you play D&D then it would make sense to have some type of license for all editions.