That's interesting, though I doubt they'll expand into Mexico when there are so many more lucrative markets in the US and Canada. Boston would be good, seems they'll go from no teams in the North East to 4 within a couple of seasons. I think that's smart. Having teams clustered together in regions obviously helps with scheduling and reducing travel - as well as developing rivalries.
It seems like at the moment the biggest constraint to expansion is actually the number of players in the US of a good enough standard! I expect we'll see more and more SANZAAR players just beneath Super Rugby standard heading over there in the next few seasons.
I'd say a Mexican team is a ways off. But it is interesting to see just how much interest there is. I've said previously that one of the biggest issues for the league won't be interest but managing that interest to ensure overall competitiveness within the league.
Regarding player depth. The league is working through that right now. It won't be too much of an issue with NY, LA and Ontario (which are apparently in the final stages of talks and look set for next season) as they bring in their own talent from their distinct regions but when the league grows to 16 and beyond is on their mind. Most of the teams have already announced and have either implemented or are starting to implement academy structures as well as youth development programs which should help address this as well as engaging more with the College side of the game.
They are also working through the foreign player limit. Most agree it should be higher at around 7 while some would like it to be open. We'll have to wait and see.