I can see the arguments on both sides, but at the end of the day I think I'll go with Mike Miller's advice, simply because I've got a lot of faith in his experience and expertise:

"The short answer for the modern BMWs with “lifetime fill” ATF: Change it and the filter at least every 60,000 miles using ONLY the factory BMW proprietary ATF."

He might be wrong, but from what I can see his track record on other topics seems to be rather good.