I'm not sure it is the end, but multi-layerd boards do complicate things. 

Components aren't going in between layers yet, still only traces. Usually the inner layers are ground or power planes for the various circuits. For example, separate, dedicated ground planes for digital circuits and audio circuits respectively.

Components, while tiny, still need to go on the top or bottom layers.

It indeed becomes harder to get boards fixed without diagrams. It would make life/repair much easier..

Sometimes you need 2 boards (1 defective and 1 functioning) to measure differences to get the culpritt.

On the other hand, (smd)components nowadays are much smaller than years ago and more difficult to replace.

Multilayering is already used for at least more than 20 years at B&O boards Broken traces between vias are one of the more difficult culprits to find

Until now I get 80-90% back in working order again (BL1, 3, etc.). I've hoped for the past many years they might release some more diagrams of obsolete parts. boards and devices.

I get a lot of owners of vintage B&O that left the B&O dealer disappointed as they were told that their beloved BS9000, BL1 or other couldn't be fixed any more. The challenge then is to make them still enthousiastic about the newer products (they often never have seen before, M5, Essence remote, Moment, etc) they see here. I've had several occasions where the owners did buy new products to combine them again with their speakers they bought years ago for a lot of money and aren't eager to spend that amount of money again, with the thought of degraded support nowadays..

I am glad there is still hope but clearly its only people who are really well versed in electronics that can do such repairs. I would imagine the time it takes to effect a repair must be quite long.