I think if you enter on a B1/B2 tourist visa, you should not be allowed to adjust status to a green card except in extraordinary circumstances. I’m not so sure about other non-immigrant visas.
K1 will obviously be an exception as substantial steps are generally taken at a home consulate.
What if you obtain a B2 visa to attend a conference in the US, and a year later receive and employment opportunity?
There is no carve out in this memo that says it’s only for B1/B2. Or that K-1 is excluded.
An entire visa class is not “obviously an exception”, or it would be clear.