I think a lot of people see Vanilla, TBC, and Wrath as this "holy trinity" of great expansions. Sure, in hindsight you could say that Wrath introduced a lot of features that would end up making the game worse over the years, but at the time it was the best of the best and when Blizzard's subscriber numbers peaked the highest they ever would.
Cataclysm, on the other hand, ended up being kind of lackluster after the initial novelty of the new and ruined revamped world wore off so I think anyone looking for a Cata Classic has to be in the minority.
However, this is where it gets potentially complicated. MoP was way more popular than Cata and that's something more and more people come to realize as time goes by, even if they didn't like it that much at the time. The same goes for Legion actually, but Legion is preceded by WoD which I don't think most people want to re-experience.
The way I see it, the near future of Classic releases has the following possible outcomes:
1. They will stop at Wrath Classic, completing the "Classic Trilogy" of past expansions.
2. They will release Cata Classic and follow it up with MoP Classic (despite Cata not having as much hype behind it) in order to maintain the chronological order of releases.
3. They will skip Cata Classic and go straight to MoP Classic. (Potentially controversial for anyone who has a soft spot for Cata)
Now maybe I am wrong in this and people actually like Cata a lot, but I just don't hear a lot of people talking about it as much as they talk about MoP or Legion so forgive me if this comes off as super biased. That's not my intention here.