Let's use market-based mechanisms to solve this putative free rider problem.

If Monero (or any altcoin) wants a monero.bitcointalk.org subdomain, its supporters must donate 10 BTC to Thermos.

That's win/win, because the altcoin gets it's own dedicated high visibility/SEO friendly subdomain, while the mothership forum gets funding at the same time as tangential content self-segregates in areas outside of the altcoin ghetto.

If we don't do this, Altcoin Jesus may take the opportunity to profit from selling more bitcoin.com subdomains, as he's already created a casino and some other goofy shit on there.