Well, currently the game isn't even up for playing yet, and no one has been able to make a guild yet, so it's hard to speak about the benefits of being in a guild, and who says there has to be a mechanical benefit? Half of the ideas for guilds on the post on these forums seem to be of the "we were alpha testers together," "we like lawtia," or simply "we're awesome" variety, and that's perfectly fine.
As for having personal guild sections in the official forums, while it would be nice I honestly wouldn't expect it personally. With how (relatively) simple it seems to be to create a guild, making a subforum for every guild seems like it would get very big, very fast. Sure, they could impose a limit on what guilds get a forum (presumably a size requirement), but that would be arbitrary and could create a point of contention between the little guilds and big guilds.
What I'm kind of expecting/hoping for is that guild tags will show up under your name, specifically during tournaments and stuff; perhaps guilds could even field official "guild teams" for group tournaments, and the results when(/if) posted would include the winners' guilds. It isn't quite an advantage or benefit of being in a guild, but I feel like it would help build a sense of camaraderie between the members of the guild and also give the guilds as a whole something to work towards, if they feel so inclined (personally I think it'd be cool to be a member of "that guild that dominates most of the tournaments," though I'd rather my guild-mates be people I like than people who play good, not that the two are mutually exclusive).
"Select the pistol, and then, select your horse."