OK since 

a) nobody from toolchain responds here, 
b) a lot of people are in favour of doing this, but 
c) noone wants to do it himself, and 
d) I dont have the time to do all the research I deem necessary to do it 
myself, 

let's harness the power of the developer community. 

https://wiki.gentoo.org/wiki/Project:Toolchain/GCC-6_keywording

Go here^, look at one blocker bug, decide why it shouldn't block keywording 
gcc-6, and comment in the list, ending your comment with ~~~~. In the end 
hopefully all the entries should look like

* bug 12345: Occurs only with -funroll-loops. User:Dilfridge

-- 
Andreas K. Hüttel
dilfridge@gentoo.org
Gentoo Linux developer (council, perl, libreoffice)