I'm just totally making this up. Not based on anything I've heard or read. Just my thought.
I don't think a CLE base makes all that much sense. Reason being, the big destination served from CLE are already domiciles. The biggest destinations served from CLE are MCO and LAS. Plus, CLE has daily flights to DEN and I'm sure they serve a lot of TPA and MIA. You don't need a domicile at both ends of a trip. You can serve the heck out of CLE with crews based in our current domiciles via day turns from those bases.
I think PHX makes more sense. PHX is a much larger market with a much larger (and rapidly growing) population. And it works great as a redeye departure airport (like Vegas). Plus, we seem to enjoy going into AA bases.