Okay here's my BIG post for why I think the ARMS character, if it's only one, is more than likely Min Min.
First off, as I'm sure you've all seen before, there was a big ARMS event that started in November 2018 (when Smash DLC was revealed to the public) and ended in June 2019 (around E3, when Nintendo decided to do the second pass according to insiders like Imran)
Its wording seemed to suggest it doubled as a popularity contest. Its final match had Min Min and Ninjara pitted together after several matches had the characters racking in victories.
In the end, the winner was Min Min.
With what I just said about the timing of this event in correlation to Smash DLC, it can almost be inferred that it was planned from the get-go, with the results gauging what character they may choose. This leads me into another piece.
The creator of ARMS, Kosuke Yabuki, is credited as a game supervisor for Smash Ultimate and has a bunch of other big positions for some of the Switch and Wii U's best-sellers
https://armswiki.org/wiki/Kosuke_Yabuki
In matches he's played, he uses Min Min in most cases, with the only other fighter used being Max Brass. His surprise performance at the ARMS open invitational with Min Min made a lot of waves, covered by a lot of YouTubers including Etika.
He even said himself in an interview that his favorite characters are Min Min and Spring Man.
https://www.usgamer.net/articles/arms-postmortem-interview-kosuke-yabuki-twintelle
We've seen characters getting picked based on developer bias before, especially with Terry and the extreme bulk of SNK content that Sakurai brought with it. So with Yabuki more than likely having a big role in picking the ARMS character as the creator of the series and a big part of Smash Ultimate's development, I could see his favoritism making some sort of influence in the pick.
So we have Min Min, the series creator's favorite character winning overall in an popularity contest for a game that was probably planned to get a character for DLC based on this event's results, ALL BEING UNIFIED BY HER RESTAURANT BEING CALLED THE "
MINTENDO NOODLE SHOP"
I rest my case.