They're rebranding, but ghetto style. Pointing the x.com domain to twitter.com is the easy part. I want to see twitter.com point to x.com instead. Because once you do this, there's no (easy) way back, engines will start indexing Twitter links on x.com, the search rank will start propagating to that domain and it'll be a mess.
And he's completely serious, and yes X is f*king terrible brand and it'll be hilarious for him to find that out in the coming months.
First of all "X" is unsearchable, so people will likely start referring to it as something like "Elon Musk's X" or god knows what. It'll make the whole site look like a joke, in case it isn't already.
Maybe his advertisers will drop in half once more. OK, I'm just daydreaming.