Quick question: if X isn’t going to be using its previous branding, and is therefore not defending or making clear/public use of it, then does that mean it’s up for grabs? If not, how long would one have to wait?
IANAL but a quick search shows in the US at least, assuming their trademark registration was current, it would take at least 3 years for it to fall inactive for “non-use”. Who knows what is left of the legal team to keep those things managed.
The problem anyone has trying to use that bird is that it effectively equals Twitter in the collective consciousness, so they would have a really hard time using it for anything that is not Twitter. Kind of why branding is such a big deal and you don’t just throw it out for the memes like the Chief Twit just did.
They still own the Twitter brand and would happily sue anyone else that would try to use it.