LSD is still available from US Refineries. It is cheaper than ULSD. It seems that stations could import either but why would they bother with the more expensive fuel? I also wonder if any Pemex can import fuel or does it have to be an independent? Pemex Franchisees operate under very strict rules. Maybe we have to wait of independent stations to be built. Other than border areas how will the fuel be transported? Trucking fuel from the USA to say PV is an expensive haul. For RV'rs the availability of ULSD is a big deal. For anyone else in Mexico it is meaningless until Mexican vehicles require the new fuel. Quien Sabe!
Moisheh
On edit here is how it could get to Northern Mexico.
Pipeline