I think Boba Fett will be the next GL because
1. referred to in the book of boba as Lord Fett (GL worthy name)
2. No Bounty Hunter/Scoundrel GL (who better than a Fett)
3. Scion of Jango was released after boba claimed the throne and repainted his armour (weird, but a sign Scion of Jango was designed for territory war)
4. There is no Revan equivalent leader for a scoundrel/BH, especially as Mando series is popping and boba beginning.
5. Because scion of jango was a conquest character they will not release another boba lower than that so will be at least equal in difficulty to acquire or a GL.
6. Synergies, Lord Fett would a GL worthy link to Bounty hunter clan (boss etc), Gamorrean guard and tusked (long awaited buff, Mando and fennec.
Now, if he is a GL I personally think these will be the required characters for this event
Bossk, Dengar, IG88, Boba Fett, Jango Fett, Gamorrean Guard, Tuskan Sharman (or new tuskan), Mando beskar, Slave 1, Fennec and series related characters not yet seen.
These are just some thoughts, love to hear comments