Right now you can just about draw a line across our country -- (think I-70): Everything south runs primarily clones, everything north runs primarily Briggs (this is true on champs as well.) We would have made it down to run at Bloomington last year but they said no Briggs (flathead or animal) champs allowed unless we brought 6 to make our own class. Same deal with the KY Burris indoor series -- our jr champs have both blue plate flatheads and animals for them -- I'm not going to get clones just for a couple of races. Besides that, I'm not a fan of the clone at all (especially all the import part specs and rules changes.) Flathead and animal rules have remained pretty much unchanged for 10+ years. The clone is not "cheap" like it was when it was introduced and caught on anymore either.
The Lo206 is a great option, but getting folks to change (buy another engine) is like pulling teeth. They were quick to jump on the clone at $300 and ride it all the way to the $1200 engine it is now, but those same folks aren't ditching their clones so easily to buy the 206 that has the same or more power for $600 an lose their competitive advantage they have with a blueprinted engine. The group at Lapel (Speedcreek) made a consensus to go to the LO206 and it worked well for them (champ car count and talk about competitive!)
Most of the midwest was on 3 hole gold animal and unrestricted flathead sr champs up until the last year or two when some tracks opened it up to unrestricted animals (for more power); and the midsouth went the direction of the clone since all their flat karts had already gone that way.
It is what it is at this point. Karting has become kind of like RC car club racing - you bring several different car/motor packages with you to the track in hopes of having a full class to run with anymore.