Neither have anything in common to warrant a slot like that.
Grandblue and Katalina are a stretch when it comes to Smash. Not only is Katalina and her popularity predominantly from Japan, but she has an extremely small connection to anything related with Nintendo, that small connection being that Nintendo and Cygames recently made Dragalia Lost and Nintendo owns 5% of them now.
This potentially also bleeds into her fan base. Her game mostly stems from a Mobile game which Nintendo didn’t even dip into until last year, so there isn’t a lot of correlation between the two. She is also younger than Bayonetta when it comes to third parties as well, since she only popped up in 2014 and would’ve been around for only 2-3 years in 2016-2017 when the DLC roster was decided. Definitely not a lot to go with for a third party.
All of these are obstacles in Katalina’s way, and they’re pretty major when it comes to character inclusions. I do like Katalina from what I’ve seen of her and she looks awesome, but sadly, I’m skeptical of her. If what Hitagi said is true, I’m more inclined to believe that it’s for a potential Season 2, as there Grandblue is starting to open a bit to the western and console gaming market recently. But nonetheless, I definitely would want to know Sakurai’s thought process fo why he chose her.