This is not personas, it's simple theming.

An actually useful persona feature would allow cookie profiles/sessions that can be run in parallel (per window, for example) to log into several gmail accounts at once, segment my search identities, etc. I've found the extensions I've used lacking (maybe I've missed a good one).

But privacy and power usage don't seem to matter as long as everybody is distracted by "OOHHH SHINY!". It's the curse of marketing to the hump of the normal distribution.