If a single founder advanced the position of the company (developed an MVP, secured some financing, etc) they would reduce the risk that the 2nd founder would face. I think in this sort of a situation, an uneven split wouldn't be unreasonable.
That being said, has anyone done it?
EDIT: founder, not "forward".
What if one cofounder is more valuable than another?
Then you split according to value and what can be agreed upon. It's not always natural to have or assume even splits.