I am aware of the fact that Mexican tax authorities are requiring foreigners living in Mexico to get an RFC, BUT US brokers and US banks, under FATCA, are only required to report those accounts that earn more than $10 in interest, but they are not required to report dividends or capital gains that you made from your US brokerage account (dividends are withheld at 10% by the IRS based on the double tax treaty the US has with Mexico.)
So don't invest on any type of investment products, i.e. CDs, that will generate more than $10 in interest.
Now, whether the Mexican tax authorities, SAT, is actually checking that information when they receive it from the IRS, I don't know. Personally I don't know anyone that has been contacted by the Mexican tax authorities regarding their US brokerage account after generating more than $10 on interest.
But if you want to follow Mexican tax laws then you are required to tell them about all the interest, dividends, capital gains, and income that you make in the US, or in any other country around the world if you spend more than 183 days per year in Mexico.
There are other countries where you can legally avoid paying taxes on all your foreign investments as they only have a territorial tax system, such as Thailand, Costa Rica, Panama, Paraguay, Dubai, and many others.
Sadly Mexico taxes on your world wide income and investments as you know.
*This is not tax advise.