In the Salesforce Developers blog post What Is A Gack? Josh Kaplan writes (my emphasis):
There are a couple of ways you can get your noted details to our internal R&D teams. If you have a case logged with Customer Support, you can feed this context information there. When your case is linked with the bug in our system, we’ll have access to your input. Be sure to mention in your comments that you are providing information that will allow us to reproduce the gack.
Another way is to post your experience on Stack Exchange. You can post the gack ID and stack trace ID, along with information on how it was that you encountered our lovely message. We will be able to find it there when doing our investigation.
I assume they will be searching for the specific GACK ID and/or stack trace ID.
I've created a GACK tag that can be added to questions. I'd like to suggest that we use this tag on questions that contain a GACK. They will appear something like:
It will make it easier to find them and indicate questions that will probably require internal Salesforce support to resolve.
It does raise the question of if such questions could be answered here. I don't think a blanket rejection of GACK based questions makes sense. There will be cases where the issue can be worked around until before it is resolved.