Why is this likely? Seems like it just does one thing well, and even that one thing now has serious competition from Youtube shorts (which are kinda better). Plus it's not cool anymore. Facebook seems to want to be a mega app but no one cares and it's just not happening because Facebook is a dinosaur.
Twitter very likely won't become Elon's X app, but I think TikTok is even less likely.
Elon has experience with Paypal. Payment and identity management is the core ingredient for an X app. Twitter gives him the user base, and he has overspent enough that everybody is aware of Twitter to easily acquire new users.
Somehow it became normal that big companies don't role out new features very often. That's not a given. Elon can reshape Twitter and turn its NASA-like development structure into a SpaceX structure. If Twitter runs like a startup it could be reshaped within months.
However, Elon could also create something like the Vegas tunnel which supposedly doesn't have the safety features to handle a fire very well. [1]
[1] https://reddit.com/r/facepalm/comments/yeni5w/elons_boring_t...