You can find the whole roadmap on the official Artery Gear Twitter.
New events and characters
Three new events with 3 new characters will be released in December.
A Carnival of Midsummer Drama part 1
Kalmia will be released with this event.
She's unique in the way that her attacks can't Crit, so she can fully build ATK and with the increased damage her skills do, basically one-shot a lot of characters with her S3. She also has a barrier that makes her harder to kill.
Kalmia despite her unique kit, isn't really a must-pull for both PVE and PVP.
A Carnival of Midsummer Drama part 2
Laurel will be released with this event.
She's a great tank whose skills scale with her max HP, so she can actually deal decent damage herself. On top of that, she can debuff enemies, provoke them and also advance her own action bar.
If you don't have a good tank yet, Laurel would be a great addition to your team, but she isn't a must-pull otherwise.
Trip with Veronica
Veronica will be released with this event.
She's honestly the most underwhelming character as she's just another single target nuker and she competes for the spot with a lot of characters. She's 100% a skip.
A lot of new skins will be released in December:
The half-year anniversary event will also be run in December, but we currently have no information on how it will look.