A chromium fork is not chrome. Why assume a fork has to accept upsteam changes?
There will be two classes of products one officially sanctioned version and the others that are used by enthusiasts. Apps or sites in this case may chose to work on one and not on others. Imagine the new wave of "works best on IE" with "best viewed on chrome variations a,b,c". Its not farfetched as some sites already do this.
As much as it is easy to maintain a fork, it is that much easy to give up or change path and accept upstream changes.