Theymos has this to say about it:
Bumping this again as I think this should be implemented before a year from now.
If someone wants to write a patch for it, I will seriously consider adding it. I believe that safely adding 2FA would be very time-consuming, so I'm not willing to do it myself or direct Slickage to do it.
Unlike last time, integrating 2FA is quite simple thanks to the abundance of such plugins, such as the one below:
https://www.smfpacks.com/2fa/Compatibility is another thing though, assuming it still supports this dinosaur version.