I think that Shimano BBs use radial bearings, so you should end up with the same arrangement as a GXP BB where the NDS bearing is fixed on the axle, and the DS is floating. If they’re angular contact bearings then I think that the lack of preload would be a problem.
They’re a sort of hybrid IIRC. An ACB, but the races wrap around like a radial bearing. Which is why you can’t get radial bearings to fit in the shells.
The standard 68/73mm SRAM BB’s seem to last just fine for me, got >1000miles out of it on the singlespeed before a freak rock killed it (slate drainage bar in the path at an angle, hopped over it and landed between crank and frame).
Hope + addapter on the fat bike though as theres more clearance and the top hat falls out of the SRAM BB, and the bearings out of any aftermarket one that doesn’t have a circlip. The hope plastic shiled acts as a circlip but needs replacing (or rotating to the non drive side) every so often.