BMW say lifetime fill to lessen the environmental impact of their products being sold, they pay less sales / carbon / impact tax as a result. "Lifetime" to them is 100K Miles - after that you (not them) pay for a new tranny. It's been the same since the E39 in the 90's /00's, but the boxes that got a fluid change at 100K and every 60K after with a filter tend to last - I should know I've had 3 and always changed the fluid and filter - the 1st 530d and I parted at 190K miles, no problems, the 2nd did a lot of driving with I think did 278K when we parted and the current 530d is at 170K - no auto problems with any but I didn't take the BMW BS as the truth as the OEM suppliers GM or ZF design the boxes for a change at 60K intervals.Thats good enough for me.
I should add however, If a box has done over 140K without ever having a change it's usually best left alone until it gives up. A lot of people that try late in the day to change usually hasten the end of the boxes days.