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.
Of course. But it would be inferior to a 30mm crank in a 68mm BB30 / PF30 shell AND a 24mm crank in a BB90 / BB86 / whatever shell. I guess I find it difficult to believe Tester would approve of it. But whatever.
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.