So far I've come up with the following baseline ideas for a second characters on the notion that one of them would fulfill a role that the party lacked or at least could use more of:
Shapeshifter - Assumes the form of someone else, effectively creating two copies of the same person; can be a Healer as Sandra or ENG one moment and then become an Aesford or Anna take during another. Extremely versatile, but doesn't bring anything new.
Druid - Similar to the shapeshifter, but animals! Has an added focus on summoning/familiars in addition to transformation and possibly some naturey-type magic. Various forms to handle various situations. Less versatile than a true shapeshifter, but has more unique benefits and abilities.
The Artist - Can bring his artistic creations to life, something akin to Sai from Naruto, or Maxwell from Scribblenauts, but cooler. As a caveat, he has a limit to what he can create at one time and its all temporary. Flexible support.
The Rapper - The modern bard, spits hot fire to invigorate his team, because I don't think we have a dedicate buff character yet.
The Robot - Big ole' robot, less versatile than Big Daddy or TBF's proposed Droid; would focus on purely one thing, maybe all offense or all defense. Highly specialized.
Donald Trump Expy - In a team dominated by overemotional magical girls and corrupted jaded has-been heroes, the savior comes in the form of a fearless mogul: Let's Make The Multiverse Great Again. More serious version of Austin, but still only about half-serious. Role would be...something.
The Honeypot - Future girl with hybrid of power attacks and healing. Based off an ER character. Also, because this game needs more sexually fluid young women. Has the butt to concur them all, so there's that I suppose.
I haven't limited my options to these, these are just the ones that I thought over for a while and believe have some utility.