And a fantail wouldn't need a larger area than that? I could easily do a tractor with a 4x4 indoor area and an area as big if not a little bigger to give them somewhere to take baths and flap around.If he can't fly he probably doesn't need a large aviary, but needs some room to flap around, and he without a doubt needs natural sunlight daily. I'd say him and 1-3 other pigeons could comfortably share a 4'x4' loft with a 2'x2'x2' aviary.
If you want to get a pal for him and don't want another flying breed, consider an ornamental non-flying breed like a fantail. They are known to be docile and friendly.
Felix is fluttering a little bit, I caught him fluttering in his cage up onto something that's about 4 inches off the ground, that's about the extent of his flying through.