Cool, thanks for your reply.
When has it been released? I've compared bitcoin core 0.15.0.1 with 0.14.1 and MAX_BLOCK_WEIGHT (should be the right constant to check) is the same.
Does anyone know where to find a document, pdf, slides, ... with a graphical comparison schema of the differences before and after segwit?
Segwit and Segwit2x are not the same thing. Segwit has already activated, segwit2x has not. Bitcoin Core does not support segwit2x so you won't find any code related to segwit2x in the Bitcoin Core codebase.