I trawled through a few more of my plugins a few days ago and contacted the developers where possible. The only people to get back to me were from MiniOrange, but you may be interested in their reply…
Glad to hear that you like our plugin
We just checked and from what we see we do support two-factor for classicpress. As the basic WordPress functionality is the same for classicpress and unless classicpress changes the authentication process I don’t think there will be any issues. We will add it to our test cases and test it with any major classicpress release.
Please let me know if you have any questions or concerns.