There is already the Super Liga Femenil de Futbol established as the Mexican top flight with 19 teams, but is there any discussion expanding into Mexico? The MFF is already paying for some of their players as is Canada and the US. I don't think it would be to far fetched to see at least 1 Mexican side (and perhaps 2 in Canada). Morelia FC could be a good option to "move up". With 4 titles since 2007, they seem to have things on the right path.
Brasil has a top flight league by South American standards, but the teams aren't that good, not up to NWSL or WPS quality. Even Santos without Marta, who was only there for 1/2 a yr, would have had problems winning against WNY, Portland and KC, just doing a roster comparison. The girls at FOZ are solid, but for example Adriana, one of their top scorers , couldn't cut it in the WPS, was a bench player. And the second coming of Marta, Maurine, only got trash minutes from Lines in WNY, and she was a star for Santos. It's not a negative on Brasilian or Mexican football, just by what standards are we talking?
Well, if Morelia want to apply for an expansion slot, they're free to do so. But NWSL isn't going to just "put" a team in Mexico because (if) they want one.
Good points on standard of play. I would imagine there would be a player draft, just as any future expansion team would have (i.e. MLS's Portland Timbers and Vancover Whitecaps). I could see the league expand in "pods". 2014 or 2015 - Vancouver / Ottawa or 13th US side 2016 or 2017 - Southern US (LA or Texas) / TBD Mexican side (Morelia or D.F.). The player pool can be stretched only so far. Hopefully women's academies will be set up with the NWSL clubs sooner than later.
Well Concacaf would have to give permission right (same for Canadian teams). Edit: Obviously also the Canadian FA and/or the Mexican FA would also have to agree.