cars are becoming more and more disposable, and almost advertised as such with older models requested for "scrappage" schemes - as soon as someone thinks they can get money back trading their old car as scrappage, it's instantly made them regard the car as just another disposable commodity...
As has already been mentioned, it wouldn't be a surprise if a car manufacturer (much like a white goods manufacturer) will try to ensure a budget vehicle will last as long as the warranty + a couple years, but frankly doesn't care too much after that, with probably a 10yr max life. Once the car is too old for their in-house approved used scheme, then they want/need their customers to update their model... On top of this, they're getting more and more complicated, with the ecu(s) monitoring and controlling more and more, so it's understandable that the manufacturer is less and less interested (or even willing) to want joe public fiddling and replacing parts - conveniently, this also allows them repeat business with elevated service/repair costs... But, it's not all bad news, modern cars are amazingly more reliable than those of 10-20 years ago - look at the M135i, it's arguably a semi-performance car, but it's service schedule is 2yrs/20k miles - that would be insane for any car 10 years ago, let alone a 300+bhp 6 pot turbo.
Down the line, it's conceivable that manufacturers will be more and more keen to stop us being able to access component/electronics... Consider self-driving cars, which are obviously in development at the moment - there's recently been a fatal crash where some are saying the auto-pilot/car was to blame. Now, consider what would happen if Tesla/whoever could prove that the owner had been fiddling with the electronics, or had extra electronics (even something like a piggy-back ecu) wired into the car's main systems - how long before they would be arguing that their safety systems could potentially be compromised by customers fiddling... so, you could well imagine that everything will get more and more locked down and inaccessible.
regarding diesel vs petrol turbos - I can't remember hearing one was less reliable than the other, but I could possibly understand a diesel turbo having a shorter life, as it would be used far earlier in the rev-range, and thus spooled more when then car is cold compared to an equivalent petrol. But, then I guess the same applies for the modern small (1 litre) engines which rely on a turbo for some oomph too - presumably they use the boost through the rev-range, instead of the old wait to mid revs and OOOooomph.
and the early debate about engine-layouts. sure, have all the ancillaries easily accessible - it's not like the engine is ever needed to be accessed to change oil filter, plugs, coils, timing belt/chain, aux belt, etc. Arguably the head-gasket may statistically need changing before some of the mentioned ancillaries. The amount of stuff that presently gets squeezed into the engine bay is frankly amazing and I can only tip my hat to the engineers - unless it takes more than 20mins to change the bulbs, at which point I would argue that critical component access/serviceability is being sacrificed... (I now remember taking ~2hrs to change the headlight bulbs in my 2012 mx5 and required removing the wheel arch liner and a hand going in via there...
