I used to follow Brian Goulet of fountain pen fame on Periscope. I think either he stopped streaming or I stopped watching when Twitter bought Periscope and stopped letting people easily record their streams by sending them to a recording service.

Since then, I've not heard one mention of Periscope in my local circles, which is only anecdotes, but my point is that there is definitely room for a startup to redo the same app idea.

For me, Byte replaced Vine since iirc some of the Vine founders were involved with Byte's startup. Byte <> ByteDance

My kids still spend hours watching Vines on YouTube. Twitter really missed the boat on that one.