So Timothy Zahn shares the intellectual property rights to the character Mara Jade, and essentially has veto power over her inclusion in new properties (movies, comic books, games, etc.).
Zahn has said he won't approve Jade's inclusion in a new work if she's present only for a cameo and/or as a two dimensional character. She has to play an important role & there has to be a commitment to giving her a fair & complex representation.
Now, I think this rules out Mara Jade appearing in SWGOH since there's nothing plot-based or complex about any of the toons we have. (To the extent that SWGOH is called a "role playing game", I think it's misnamed: your "character" is a cantina gambler and your only role playing is developing your roster - might as well call Madden 2020 an RPG since you also manage your roster using a slate of pre-approved characters in that game.)
However, if developers earned Zahn's blessing by writing an interesting role for Jade in a Star Wars TV series, she might then be able to make her way into SWGOH.
There are many opportunities for this. Mandalorian Season 3+ could include Jade either pre- or post- meeting Luke in Heir to the Empire (the timeline isn't entirely clear to me, but I think that Mando takes place 8-9 years after the Battle of Yavin & therefore is almost exactly simultaneous with H2E. There are 3 TV series currently in development. One is said to be "female centric" with few other details, but Wikipedia includes this bit:
According to Variety's sources, it "takes place in a different part of the 'Star Wars' timeline than other projects." In early November, Headland expounded that the series would be set "in a pocket of the universe and a pocket of the timeline that we don't know much about,"
That makes it sound like it wouldn't work, since we've explored the entire timeline from Ep:1 through Mandalorian (8/9ABY), though it's still vague enough to be possible. "Pocket" could be a small portion of the timeline, and Jade's backstory as a child during the early days of the Empire could work if the series takes place in the small void between Ep3 & the Rebels Animated Series.
One better candidate is the Cassian Andor series in development. It's said to be "darker" and comes from a period where Jade is already a fairly high level operative for the Emperor, but maybe not yet high enough to be the Emperor's Hand. Which is to say, she might be a powerful nemesis to someone like Cassian who wouldn't be high-enough in profile to receive the direct attention of someone like Vader or Tarkin or Thrawn.
The last series currently in development is the Obi-Wan series (starring Ewan McGregor!) taking place half way between Ep3 & Ep4. Jade would definitely not have been an Emperor's Hand at that point, she'd be too young, but she could have her backstory elaborated & Obi-Wan would need force-sensitive/force-talented enemies as opponents.
Now, I don't know if she'll show up in any of these, but one intriguing possibility is that Jade's life & career span literally **all** of the shows for which we have clear timelines, and she's not yet excluded from the fourth, so they could actually use her as the one character that appears in all the different shows and helps unify the story arc. She wouldn't be the main character in any of them, of course, but she could have an interesting, complex & compelling role in each.
So this is intended as an invitation to speculation. Knowing that we have to get permission from both Disney (who holds the main rights) and Zahn (who holds a share in the rights to Jade), who thinks we'll see Jade in an upcoming season of The Mandalorian or one of the 3 shows in development?
And if we do see the character approved for use in one of those shows, it will be an interesting legal question whether that means she could then be used in SWGOH without further Zahn permission or whether we're essentially barred forever from seeing Jade in this game because of Zahn's veto rights & insistence that she be portrayed in a major & complex way when neither of those things is possible in a game like SWGOH.