There's a lot of awesome suggestions here. For me, I'd love:
DC-
CW Black Lightning
CW Supergirl (and others from that show)
Loads from Flash, Arrow and Legends (Savitar especially)
Comic Kid Flash (No clue how this hasn't been done yet)
Comic Black Canary
Comic Ras al Ghul (just think he'd look awesome)
Marvel-
Comic Hawkeye
Comic Black Widow
Comic Scarlet Witch
Comic Thor
Other Spider-man villains from the comics
Other MCU characters yet to be made (Iron Fist, Ghost Rider, Fitz, Simmons, Agent Hill, Whiplash, TFA Red Skull, Ironman Mark 5, Iron Monger etc.... the list goes on)
And updated Nick Fury would be awesome too
I imagine a lot of these Pops will be made in the future, but we just gotta be patient (easier said than done)