Frankly, All ATs could use new APP/PPPs.
Electric for Tankers and Scrappers.
Psionic for Blasters
Ice for Defenders
Archery for Controllers (Some Archery Attacks, a defense toggle, maybe Boost Range or something)
New Patron for Villains (no idea who, probably someone who would have to be added in)
Ideally, what I would like to see is a parity between the sides (particularly with GR on the horizon) were Heroes get Mentor Power Pools (MPPs) added in as a mirror of Patron pools. Sets themed based on the Mentor chosen and unlocked by a story arc, possibly having to do specifically with that Signature Hero's backstory.
Then have generic Ancillary Pools added to villain side just like those on Hero side, themed based on whatever element they are.
This way archetypes from Both sides get access to elemental themed APPs automoatically no matter what side they are on, and then you can unlock EITHER the PPPs or the MPPs for your AT, depending which side you run the arc for.
@Oathbound & @Oathbound Too
I was just suggesting, but I thought maybe Tanks can have Electric Mastery and a new Shield or fire mastery for the pool..