Void G requirements

[Voragath]

Just took a new warrior in our guild who was flagged for void e through all of the tower events and she's still void e. My guess is, you have to do the 3 kora raids as well. So, it seems Kora will flag you for F, then tower will flag you for G in that order. Can't skip the Kora events. We'll likely get her through Kora this week, so I'll let you know if that puts her in G or not.

[Igniz Facere]

I can verify this, i watched my druid progress. Fresh from E with all group/solo tasks, no raids.
After Kora, she was in F and after Tower she was able to enter G

[Mindrix]

Tower doesn't work like like the other voids. You need to have F done for G to do anything. You can do F via Korafax raids or group missions, from what I've pieced together over the year.