Some well reasoned speculation over at PJ Media goes:
Obama has put Keystone on hold indefinitely;
Obama thus calms some environmental whackos;
Between now and September or October Obama will find another bone for those whackos; and,
In September or October Obama will ok Keystone just in time for the Senate Dems to have something to crow about just before the election.
That sounds about right to me.
And then in December use some excuse to shut down construction.