Most news sites speculate that Visa is likely to follow. OF probably has industry connections that are giving them a heads up.

It's in Visa's PR interest for these high visibility events (like OF's ToS Change) to happen before Visa announces their ToS changes.

They expect VISA will follow suit.

Source? Or are you just assuming?

I believe that it's an assumption for now, but a reasonable one to make. I think it's unlikely that Visa exposes itself to legal risks where MasterCard is not - why give your competitor an edge like that?

That assumes that there actually are legal risks, and that there isn’t more money to be made by continuing to process these payments.

For Mastercard and Visa the money to be made is a rounding error on a rounding error, there are lots of other industries that don't have the same PR risks as adult content does.

Probably because visa will be enforcing similar to rules soon too.