[thejeff]

Well that's sort of the kicker.
Most games are played without R'lyeh because it's really hard to challenge R'lyeh in the water. Boosting another powerful nations ability to do so might just mean Mictlan is the next too powerful nation, or it might mean R'lyeh can be used more often because it's got more valid opposition.

I haven't done a lot with Mictlan underwater. Is it really that powerful? It's got capital only sacreds and mages. For anything else it has to rely on water breathing items or indy recruits. The LA Atlantis underwater troops aren't really that special, though the Unsleeping(?) have good MR.
The Mother is just an expensive H2, could be thugged, but Mictlan's usual bless doesn't work to well for thugs. The Father is useful, but doesn't really add a lot for Mictlan.

Ideally, I'd like to see someone able to challenge R'yleh for control of the seas enough that R'lyeh gets used more often.