It's whatever, lol, not something that's really going to be affecting me either way. =P I won't be wearing them to the beach, and I won't really have to see them on anyone else, because Oregon beaches are too cold for swimsuits most of the year. Even in the middle of summer, one might want a little more coverage, because of the wind chill factor, haha.
Thongs should only be worn for your boyfriend/girlfriend to see. Not on the beach 0_o but that's just my personal opinion.. Even if you're single its a little...'slutty' in the lack of a better word. Sorry, not trying to offend anyone that do wear them.
I don't think thongs will ever be mainstream on U.S. beaches. Too revealing. Plus, kids around. But it is considered normal in many other countries. Cultures are very different from place to place. I don't really mind seeing or not seeing thongs on the beach.