Yes there is an argument to be made whether pardons can be made in advance.
It doesn’t make sense to do it in advance imo. If pardons can be made in advance why have laws? Can 0bama simply pardon everyone right now ... and it would be over?
Maybe, but it also might spark a general political or civil uprising so it is risky. However, more likely, I think, is a blanket pardon for "all crimes committed or which may have been committed" issued on the last day of Obama's Presidency.