I'd be quite cautious. Our US exhaust / emissions system is a work of art with complexity.
There are approximately 8 sensors devices in the exhaust tract of our 335d. Pre and post DPF temp sensors, O2 sensor, Pre and Post NOx sensors, SCR metering valve, SCR temp sensor, etc.
Whatever soot / deposits you suddenly jar loose from the engine will now end up gumming up your expensive sensors.
Coming from gasser cars, anytime a silicone product hits an O2 sensor it is shot. I remember way back guys were running different additives or flushes to their engine only to then accidentally kill all 4 O2 sensors.
If it were as simple as running some cleaning agent through the engine, wouldn't BMW do that instead of pulling the head / intake? My cautious gut instinct is that they know an engine flush could prematurely foul the DPF and other emission components. (However I hope I am wrong as it would be an easier cheaper solution to avoid soot buildup)
Just a heads up.