The characters are currently defined in-game as either Defender, Attacker or Supporter, so if anything like this were going to be introduced it’s very likely those would be the categories. The issue with limiting selections based on broad generalizations like those, to me, is that Battleborn is awesome because of how crazy different each character is from the next and how vague those classifications really are, particularly when factors like helix selections are considered.
Toby, Attikus and Montana are all “Defenders”, but one is an area-denial artillery emplacement, one is a late-game melee wrecking ball and one is a mid-range slab of bullet-eating beefsteak. Their individual impact on the game is very different, and I don’t think having two (or three; go crazy!) of those guys on a team would create much of an overlap in role or effect, or necessarily leave you lacking in other areas.
Similarly, Miko and Reyna – while both being Supporters – have vastly different combat roles that just happen to both center on team co-ordination. And having both on a team is a thing of beauty.