Well, that feels like a different circumstance to me. II, III, IV and so on are significantly more understandable and readable compared to... MMXXIII or what have you.
(Whether there will be more Skywalker Saga films is not something I’d like to speculate on.)
Star Trek V is the one with "Shakespeare is better in the original Klingon".
The movie you pointed to doesn't exist; it's a conspiracy by IMDB and other parties to make you think there really was a Star Trek V, when in fact there was never any such movie. If you believe there was, then you're a crazy person who probably also thinks there were sequels to The Matrix.
They’ve already decided: “whatever we feel like for the film in question"
> but when in the modern age when your new movie is “Ant-Man and The Avengers CCXCIV” it gets a little ridiculous.
None of the Marvel films have used roman numerals, and, IIRC, in the MCU only the Iron Man films and the Guardians of the Galaxy films have used numbers (and Deadpool, which wasn’t really MCU until the next one, also uses numbers) outside of early working titles. Most of the other “series” within the MCU (Thor, Avengers, Captain America, Doctor Strange, Black Panther) have used subtitles after the first (or in the case of Ant-Man, used a longer main title for the second, and a subtitle to that for the third).