Surprised nobody has posted this yet...
Anyway, I don't think he could've become Emperor because it's not in the man's character, the closest you can get is something like Julius Caesar where he's often mistakenly considered to be the first in a line of Emperors that started after his death, as a result of him being Dictator-for-Life for a while.
That I could certainly see Jackson both becoming, and getting away with. New England might end up seceding as a result (or perhaps the POD can be that they did to start with in the 1810s a la Decades of Darkness). Without New England Jackson can basically rule supreme as a strongman on the back of his popularity with the common people against the establishment.