Sulphur wasn't an excuse but a fact. It was a metallurgical issue.I have found the opposite to be true. BMW engines, regardless of type, year etc. seem to sludge up more than others I have worked on and own. I am not talking about just my experience either, I know retired techs who have seen this also, plus the internet shows multiple examples. The highly evolved service indicator system should be able to compensate for abusive scenarios, and pull back OCI accordingly.
My position is this:
BMW used the sulphur excuse for their V8 engine problems in the 90s, which may have actually have been the case. I don't buy it for this.
Somewhere in that firm they have decided on a philosophy of long drains and lifetime fills.
Lifetime fills in GM and Aisin built transmissions that other firms use with more reasonable (realistic) intervals.
I love BMW and think their cars are excellent. But, they do make mistakes, which somehow, they never admit to.
For the enthusiast, BMW recommendations should be considered to be for a different purpose than solely vehicle longevity.
I mean fluid type as well as interval in the above statement.
When people only recommend going with a fluid that meets the cert, I think that is certainly a safe bet, but is also not the end of the discussion, especially where BMW is concerned.
BMW engines don't develop sludge unless the oil hasn't been changed on time or the wrong oil was used. IMO there was less margin for error on a 15k interval. IMO BMW also expected the N20 to make the same power as the NA I6 it replaced so the demands of the TGDI I4 were higher.