There aren't many GL worthy characters lying around.
I mean, Darth Krayt, maybe? He's certainly legendary to a certain non-human population of the galaxy.
The Great Old Mothers triumvirate? (I mean, if they can release that huge Jabba, they can release a single character that's actually 3 toons standing close to each other.) They probably have power worthy of it, but I doubt that they're "legendary" beyond the NS faction.
GL Mace Windu? I mean, yeah, kinda? JMK is based on Kenobi **after** Mace is killed, so there's room, I guess. But he'd be the 2nd Republic GL and that doesn't really work.
GL Ahsoka? I mean, no. She's awesome and I love her to death, but she's not JML and she's not supposed to be. I guess in theory we could see her gain in power but still decline to be a Jedi. That might explain the lack of Jedi in the timeline when JML is organizing his school and during the sequel trilogy. But we haven't seen that power level out of her yet. And if we did, what faction would she lead?
There's room for a LS Droid GL, but the only one who makes sense in lore is R2, and... what would you base his skill set on? In theory they could come up with a droid we've never heard of and make that our new LS Droid GL. I'm not actually excited about the idea.
The High Republic is a time period I know nothing about, so there might be legendary personalities from that time (I mean, logically there WOULD be legendary personalities from that time) but I don't know them and I'm a pretty big SW fan. Not obsessive, I'll grant you, but pretty big. That means that they might justify the GL tag in theory, but they wouldn't *feel* justified to the majority of fans who play this game. (At least if I am representative.)
All in all, I see GLs as mostly played out, now that we have Leia.
We will still need new super-characters, of course.
But
1) Omicrons allow the creation of a character that can be a super-character for a specific purpose, like in a raid or on a new Conquest planet or whatever, without actually being a GL or GL equivalent.
2) We don't have to call them GLs. Pick some High Republic toons that are worthy of being minor gods in the game and call them "High Legends" or whatever. Or "Historic Heroes". I mean, anything works.
We had legendaries and hero's journey and galactic confrontation characters before we ever had GLs. CG didn't just keep adding the most powerful toons to the old most powerful category. They created new categories.
Retire the GL category. Create something new. Constantly trying to come up with toons that are equal in galactic historical importance Lord Vader just cheapens the category.
These toons are what they are, and they're harvested primarily from the movies we have loved. Other toons can come along and be powerful in the game without being equated to Leia and Luke and Vader.