Can you imagine Tester pondering how to put an inferior 24mm axled crank in to a 30mm receptical? I can't.
You can put a very good Shimano 24mm crank into a larger shell allowing for decent size bearings, unless you use one of those "lump of metal" adaptors.
What about BBs for BB30 Shells and Shimano road cranks (well, rotor).
I'm thinking Wheelsmanufacting With Enduro angular contact bearings.