The guibo and the u-joint look perfectly fine, so I think you're on the right track looking into the center support bearing. Personally, mine was ruined because after uninstalling the driveshaft to install a new clutch, I bolted up my CSB upside down. The rubber portion of mine was ripped all the way through, where yours seems to be intact.
Yours is oriented correctly, but I'd still be uncomfortable with that much play in the center support bearing. Ideally, that should not have any play. And would make sense considering the sound on hard braking if the torn rubber is allowing the driveshaft to shift forward.
The only part that doesn't make sense to me is that you're getting no vibrations under heavy acceleration. From all my research, that should be happening if your CSB is shot or nearing the end of its useful life. Regardless, I'd probably just order a new OEM BMW CSB, throw it on there, consider it maintenance, and see if that fixes things. It certainly wouldn't hurt.
Put the car in neutral to rotate the driveshaft.
Also, I wasn't aware of any driveshaft recalls. Why exactly was the guibo originally replaced? Was it an aluminum version?