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.

2FA is apparently fairly difficult to integrate into SMF (the current forum software).

2FA is going to be implemented in EpochTalk. I suppose we'll all be able to use it once the forum software has been replaced:

https://github.com/slickage/epochtalk/blob/master/app/templates/login.html