It's no stretch of the imagination that this will replace many, if not most app ui's. For the time being there's still some programs that are much better off with a dedicated interface, but the future where the starting point for most day-to-day computer interactions is a unified natural language text input is very near.
It's striking to me how close this matches the depiction in the movie "Her".
Messenger apps like telegram do have an opportunity here, but I think the most likely way for this to play out is that apple and google will eventually make their assistants the front and center way of interacting with your phone and their won't be much that messenger apps can do about it, even if they are substantially faster at implementing this.