This would be terrible UX, in addition to devaluing questions that are timeless in nature (like theory)
As far as "theory" questions, such a designation could simply be another moderator privilege -- high-rep individuals would have the ability to vote to prevent a question from decaying. Perhaps an additional requirement would be that the question must have been transferred to Community Wiki.
> You haven't explained why "this would be terrible UX"
What's with the tone? I'm not your child
But it's a Q&A site, not a point-gathering exercise. Leave the displayed score of the answers/questions but decay the benefit the author gains from it.