You'd need 1/4"/foot to the waste line and vents run. Better to bite the bullet and break the floor for an underfloor connection. The shower drain trap would likely run 4-6" in depth plus the thickness of the new subfloor and the height drop it needs to reach the drain, plus the thickness of the shower floor pan which must also be sloped 1/4" per foot to the drain. The height is likely to be both cumbersome and may be problematic with your typical basement ceiling height. My unprofessional opinion.