Congrats on your 200k miles!
I am a new owner of an 05 X5 3.0i with only 45k miles on it (still under mfg warranty for a couple of more months) and must say I never really doubted the engine could do that kind of mileage... may be I am too new and naive, but I am into motorcycling and in motorcycle world, BMW engines with 60-80k miles are considered to be in their early-mid life.
I must say I was worried about all the other expenses around this car, but given the way it drives and feels, I don't think I will mind the extra expenses, at least that is how I am feeling now.