Giving this a bump because I would really like to see this feature as well.
If I had the skills I would submit something back to the project code wise to help move this along but I do not.
The first forums software to have this feature easily out of the box is the one I am likely going to be going with. I hope this is the one that has it first in all honesty as this seems to be the best designed software I have seen yet for forums.
My audience demands 2FA for all such things and sadly it appears I will be forced to use bbPress (really, really, awful) because it has support for Authy via a WordPress plugin at the moment.