I just came across this topic whilst searching for previous topics on no-frills airlines and actually think it would be quite interesting to see any new no-frills startups that use a similar business plan to Gol - with the typical no-frills formula but across South America.
I think the only place where a low cost, no frills airline would work right now would be Chile. The only competition to LanChile is Sky Airlines, and so there is a ripe market for a new airline.
Alternatively, I think Argentina could be a good place to start a new no frills airline. There are a few badly run and expensive carriers like SW and AR, that could do with competition.