This question is very subjective, but anyway...
Is it possible to rank higher than Google for the keywords "webmaster forum".
Yes, I imagine it's possible, but extremely difficult. You're going to have to build and market something that's bigger and better.
Millions of people use Google products, millions of people have queries regarding those products and
productforums.google.com have become a go to resource.
But step back for a moment. This is an incredibly generic search phrase - who/what are you thinking of targeting exactly? For example, search for
HTML webmaster forum and Google has now gone from the first page of results.
Often users find forums when they are trying to solve specific problems. So, they are searching for specific phrases, not a generic catch-all phrase.