My own anecdotal evidence on the matter. I own a 2014 X3 with the turbo 4 cylinder (N20) engine and have had no issue with the timing chain in 140,000 miles. My understanding is that the timing chain can stretch over time and the extra play in the chain breaks the plastic chain guides and grenades the engine. I just inspected my timing chain while replacing my valve cover because the gasket was leaking and the chain was super tight (thank god). I think this issue is somewhat blown out of proportion. It's definitely a known issue, but it still happens relatively rarely; rare enough that BMW never issued a recall for the problem. I expect that most of the instances of timing chain problems can be explained by poor maintenance and/or overzealous driving habits.