I believe SEO is one of the main things that hinder client-thick architecture adoption for many apps that depend on their content showing up on search engines,

I believe SEO is one of the main things that hinder client-thick architecture adoption for many apps that depend on their content showing up on search engines, especially among content-driven websites (e.g. Stackoverflow, Quora, etc.). But I agree, all signs are pointing at the direction of thick-client implementations and eventually search engines will solve the indexing problem.