Mine is checked annually, no probs so haven't thought to pre-empt it as a result. My thinking goes back to the time I visited ETA Motorsport as they are located near my sister's house so convenient to pop in. They said they have had track built E46 M3s with no subframe cracks, yet normal road ones do get cracks, later model year examples fare better, and convertibles have a stronger support back there anyway so less affected still. I think I may have flipped the head on the coin in this area, although tails in other areas (rod bearing failure and the other maintenance items I've addressed over the years etc).
But yeah general consensus is that all boot floors will crack, with a few exceptions that boils down to luck of the draw.