Want to fill in my reverse sloped driveway.

I have a reversed slope driveway in my back yard that leads to an attached garage. I'd like to fill in this driveway and seal off the attached garage. I have a large detached garage, so the tiny attached garage is not needed. If the driveway was filled it would nearly double my useable space in back yard.

How feasible is this project? Any ideas on cost? I'm curious about issues with drainage because I have a sump pump at the bottom of the driveway now. Also any other issues I may not be considering. Any insight would help. I've attached pictures for reference.