Yeah interesting. I mean know one who knows anything about the topic would include Cantonese in the topic since for a long time the PRC have deliberately marginalised that and a number of other dialects/languages so the idea that Cantonese would take over is as relevant as saying any other dying language could take over.
Mandarin on the other hand, as a speaker of it, is one of the easiest languages to learn. People assume that it is hard because of its steep learning curve, however Japanese or Thai (which I also speak) are far harder. Further more Mandarin is fast developing into a Kanji free language, something Thai and Japanese won't do due to the presence of sanskrit based language or katakana, hirigana and kanji.