I know this is an F30 thread but recently had a cylinder misfiring at 41k on my '16 435ix. Was replaced under warranty after 3 visits to the dealer. Car is stock with just MPE installed. I came across a lot of posts about misfiring cylinders and coils failing within 30-40k miles. Even on relatively newer cars.
However, my previous car '14 328ix never had a single issue until I traded it in at 42k miles and I drove the hell out of it all the time, pushed it to its limits a few times(hitting the limiter)
Also, I don't think the forums represent the correct estimation of reliability or the lack of it, I know a lot of BMW owners who never visit any forums, some of them are car enthusiasts too.