Obviously for a timing chain the engine would have to be pulled or transmission dropped. I think a full timing chain replacement is somewhat unlikely, though who knows as there are not a ton of high mileage engines to glean data from at this point. The far more common concern is repairing or servicing the VANOS system which is what controls the variable valve timing and will require special tools to complete. From what I have gleaned from the BMW community, expect a VANOS expedition in the 100-120k mile range and it can be done without pulling the engine. It's not cheap, and is complicated by the fact that the VANOS components will be located under the cowl, which is certainly disappointing, but not necessarily a deal breaker for me anyway.
Do I wish it had a simple naturally aspirated motor produced by someone other than BMW? Of course. I also wish I were better looking and more charismatic, but I deal with what reality gives me.