Cole Goldberg said
How about a route to Richmond, Virginia? … I could see JetBlue or Frontier adding this route.

I think Frontier will add CLE routes to some of their spoke cities that now have flights only to DEN or TTN for better station utilization.  As a Frontier expert on another board said, Frontier now shows Cleveland on their system route map with bigger print and a bigger dot, for whatever that's worth.  The problem is Frontier doesn't have any aircraft deliveries coming soon, although they have bought used A320's in the past and could again. A future Frontier with business-oriented hubs in DEN and CLE makes quite a bit of operational sense. 

JetBlue will be receiving A321's this year for transcons, freeing up A320/E190 aircraft for new flights, maybe BOS-CLE-FLL? Richmond would be a major commitment that it's hard to see them making.