in general, the conference presentations of the past few years are up-to-date and there're some mailing posts and blogs on certain features as well. are you looking for some specific?
the non-x86 arch specific features have not been documented except for spender's blog on KERNEXEC/UDEREF on arm and soon another entry on REFCOUNT/powerpc. so your best option is to ask your questions here and i'll answer them .