Exactly. It sounds elitist as all hell, but there is a clear difference.
I wouldn't even say "elitist". There's a fundamental difference between small XML-only GameData or Lua-only UI mods, larger ones that mix XML, Lua, and art assets, and huge FfH-style total conversions that replace the entirety of the database. If nothing else, this sort of categorization would be useful simply to know how likely things are to conflict with each other. Small XML mods almost never conflict with anything, mid-sized things will have many conflicts but most are workable, and the big FfH-type things are basically standalone games.
Though, you're incorrect on one thing; That forum has more than Thal's mods. There is at least one team forum there, for Eden (no, the public can't see it, but I assure you it's there

), that predates Thal's forum.
Maybe so, but without being able to see those other forums, a user of these boards gains no benefit from the distinction. The point I was trying to make, and that others have said before me, is that the most active large-scale mods should be moved into separate forums if only to keep the threads from clogging up; the Projects area is just the most obvious choice. Being able to have separate threads for Policies, Units, Wonders, etc. helps tremendously.
Then have "Trusted" or "Gold" or whatever you wish to call it; have this multiple prereqs. Payment, prior mods, etc.
Payment is obviously a major problem. Given that Firaxis' employees are paid more per hour than I am, and given how many hours it'd take them to go through my mod to certify it as "safe", there's no possible way the price for that service could ever be reasonable at market prices. So Firaxis would have to basically subsidize, charging a token amount just to keep the riffraff away and paying the rest out of their own pockets as an advertising expense. Oh, and updates: every time I come out with a new version, would they have to recertify that before it becomes available for others to download? I've updated my mod about 35 times since last October... or would it be that once my mod is certified once, I'm now a "Trusted" modder and can update as often as I feel like?
Probably still a good deal for them, but that brings us to the second problem: why would I bother? I mean think about it. I've got a mod here, on CivFanatics, where it's hosted for free and I can update it whenever I feel like it without major headaches. While I like the idea of other people playing my mod, I'm not going to pay a huge amount to get the "official" stamp. Heck, the main reason I made my mod in the first place was so that I would enjoy the game, myself; the feedback from other people playing just makes my mod that much better when I do play. I'm sure I'd get more people playing it if it were on the Mod Browser, but I'd get even less useful feedback that way.
Basically, I just see them going the DLC route instead. Ask the people who made the most popular mods what five XML stubs, Lua functions, or art assets they'd each like to see added, make those be unique to those mods (so that the version they sell is markedly better than the one you can download for free), and release a "Developer's Choice" DLC pack. Of course, once we have the DLL this might not be possible...