Cassian might be my least favorite character of the Disney era; I thought he was totally one-note and boring in Rogue One. A series could really do a lot to change my opinion by fleshing him out, though, so I’m on board. Plus, I’d never say no to the possibility of more K2.
EDIT:
I’d love to see K-2 again!
Never got into RO because of the poor characterization (besides the robot). Bur while I’m not a fan of Cassian now, the six years old line could give way to some superb stories.
I’ve been beaten to my own opinion.