There are many countries who will not abide by these rules, any large decent exchange will simply pack up and move. It's not like they have to be situated on their land, servers and data are easily transferable.
that might work for a year or two until countries start getting blacklisted by the financial system. the first FATF statement on compliance with these rules is in june 2020. they may start blacklisting at that time. at the latest, it'll start happening by 2021.
the larger the exchange, the more difficult it will be to operate in secrecy or simply pack up and move. local governments will start targeting and shuttering noncompliant exchanges once the FATF brings the hammer down.
i doubt bitmex and similar exchanges will keep operating this way at that point.
Doing business as a cryptocurrency exchange these days is following all the rules as imposed by the government especially if one is based in USA or accepting transactions from American citizens. I am not anymore surprised if all legitimate exchanges will follow this proposed rule of exchanging or sharing customer information with each other as this is being done with traditional banking system. Soon we will witness exchanges being burdened by the same banking rules by the government and refusal to follow means one has no privilege of doing business. Well, as for me, this can be the eye-of-the-needle test for many exchanges...which in my opinion can be better than experiencing an exchange which just evaporated without a trace. Again, this is my opinion.