Actually, it IS better to have all these on one big device, as the wear is then spread across more flash blocks, unless you plan on introducing more chips with different technologies (=higher cost + more space + higher complexity).

Anyway, if this was a real problem, we'd be flooded with N810 users with dead internal cards by now (as the N810 is swapping on a 2GB flash device = 16x shorter life span than the N900 on equal tech and number of writes).