Yes, I have thought about that. But the cutouts would really limit the usability for most people. Everyone would have different things they want to carry and cutouts would limit them, so I've been avoiding cutouts. I have everything on order, so I will be experimenting with it when the materials get here.
The foam will probably be lower than the edge of the case, so the lip would keep things from falling out, but I've also been working on mounting an elastic strap (like in cigarette cases) to hold things in place. Or possibly just cutting slits into the foam, maybe. IDK - I have to play with it!
As far as cleaning concerns, the foam is a neoprene, closed cell foam, which resists moisture and oil. Additionally, the adhesive I ordered is a professional grade foam adhesive for mounting foam. It's made to withstand moisture and high heat, so it should withstand washing in the case. (Not in the dishwasher, though, because I don't believe the case finish is dishwasher safe.) So, drip in some dish soap, run under the tap to rinse and blot dry with a paper towel.