Without knowing it, you've walked right into the middle of a minefield.
The issue of what forums/lists Glorantha and HeroQuest are discussed on has been a very thorny one. In the past there has been considerable dicussion and disagreement surrounding the creation of new discussion forums, and the moderation policies for them. While your offer to put in the effort and resources for a new forum are praiseworthy, in practice it's potentialy a very divisive issue.
having said that new forums do emerge frm time to time. The Forge (www.indie-prgs.com) has a HeroQuest forum for example, but that site has a community and culture of it's own, so that forum is a gret place to dicuss HQ in the context of that community. Specialist forums can add value to the community, especialy if they cross over with another existing community of gamers, creating interesting synergies.
Setting up 'The Gloranthan Forum' is risks being interpreted as a power/turf grab, regardless of the generosity of your intentions.
Best regards,
Simon Hibbs
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