It is suggested that BO is paying back debts, in other cases it is suggested he is trying to raise funds using whatever, and some are suggesting he is selling state secrets. Most likely just attempting to undermine the President.
Maybe all the above
I’ve seen speculation that BO is not shadowing (as in following), but is preceding POTUS.
In either case, I agree with your second paragraph.
One other possibility is that BO is looking for a place that will grant him asylum.
(Maybe POTUS is shadowing BO! JK.)