They can already go a couple of miles inside the country. I do hope that all trucks, regardless of country, are inspected for safety and illegals.
My law: If a Mexican truck is the cause of an accident/smuggles drugs/smuggles illegals, driver goes to jail for vehicular manslaughter/criminal negligence, company pays all expenses involved + $50,000 minimum fine(collected by tarrif/seizure of goods from company), Mexico pays for jailed driver and any others we wish to detain. Same for any countries trucks.