Trying to frame it as one discrete change is just going to get people needlessly emotional (if it hits the 'technews sphere' where editorializing and sensationalism reign supreme. Everyone seems level-headed in the mailing-list discussion for now.)
Specifically, there is worry that removing GCJ and associated test suite will exercise fewer code paths in the collection, and the claim is that adding go will cover one obvious subset of these (-fnon-call-exceptions).
If you read down the thread further, Ada has been suggested as a better replacement than Go to keep test coverage, since it builds on more machines and actually does a better job of exercising otherwise unused code paths.
I'm not saying it's true or anything. Just calling it like I see it...
There are lots of those for Java, but OpenJDK isn't one of them.
I still remember downloading Blackdown Java.
They clearly recognise the test suite takes too long to run, but it takes time to fix.
Other backends are not as mature.