Listen, in general I myself understand the chances of Rex being playable aren't incredibly likely. People have different interpretations of how things were worded. I happen to have a different interpretation. I simply don't think it's entirely out of the question.
I must say though, I love how some people are already making "rules" about DLC despite the fact that many people, on this board, got BTFO this entire speculation cycle. It's as if no one learned anything about how things changed between Wii U and Ultimate, and are still looking at things all the same way, even though they've all been basically disregarded. We even have some people (won't name names but eh) who are still ruling things out or making people look stupid for thinking of certain things differently.
Like there was literally discussion the other day about how Sora is a "Disney rep" by law. "Reps" is a fan term. There is no law that specifies who is "rep" for which company. They're video game characters. If Sakurai wants to try and acquire them, he will try and acquire them for the game.
In terms of DLC, I have to wonder if they'll actually go beyond the Fighter Pack. We're like, actually, getting close to the bottom of the barrel. Not that Piranha Plant isn't hype (I actually love the character and think it's amazing), but it's a generic enemy. After we get 5 more characters, we'll be at 80 (81?) characters. If Vergeben is to be believed, we're getting 2 3rd party characters. If Mystic Distance's source was right about Lloyd having a good shot at DLC, then that's 3 of 5. Then we have the SE character, and that makes 4/5 as 3rd party.
That leaves just one character.
Granted, I'm personally of the opinion that I won't move on from Ultimate if the next Smash game is a reboot (and in a different genre, no less) or makes significant cuts. This game is just too good content wise for me to play a Smash game that doesn't have all of it, and honestly, even if I don't get Rex, I get something rather than nothing.