I definitely think the IRL subforum is rather irrelevant since it's either a discussion or general talk that's just about life. It could be done away with.

As much as I find it confusing sometimes that the art shop and art post are two separate things, without other major fanangeling, I'm not sure it makes sense to combine it all. Shops are commercial. The rest is not. I do think the Nook and Post forum should be combined though.
Art shops could theoretically be combined with shops, freebies, and auction in the main forum with tags, and requests in a subforum though. Basically separate sell and buy.

About the rp forum though, I'm rather partial to how organized it is. I also think it's absurd. I do not like the idea of combining 1x1s and group if the genre subforms are combined. I know certain of those genres have almost an entire page of active day to day rps so even with a visible group tag, it could easily fall off the first page before anyone sees it and groups rely on being seen. Without lumping them all together, it would work just fine, but it's one or the other. Most of the genres don't have any active groups so I never even look there. If they're with their 1x1s, I'd definitely see them more. I find sites with just Request/OOC and then ALL RPS to be a mess.
I do think the genres could be condensed rather than fully combined though. Say...
fantasy/sci-fi
modern
historical
fandom
unclassified

However it is done, I do think this site has subforums all over the place that could be condensed, but I don't want to lose the organization either. It's just as hard to find things if not harder that way, just less spread out.