There is definitely a wave that is happening on other video sharing platforms but I suspect that it won't be a big sea change as the content on YouTube is deep and embedded so the YouTube still casts the widest net. Tik Tok and Astronaut.io are interesting but as I type this post word from a 15 year old teenager says that the alternatives are boring so the attention span required is short. The alternatives are entertaining but will really only be a threat when learning takes place on them. The demographic is different and learning will need to take place it 15 seconds or less. It might also be interesting to note that there are approx 200 variables Google looks for when deciding who rides the wave or not.