I've asked today the following question What is fairly new theorem one can teach (and prove) to an undergraduate student?
As @quid mentioned in his comment, a very similar question was asked on MO.SE, see https://mathoverflow.net/questions/129759/modern-mathematical-achievements-accessible-to-undergraduates.
If there hadn't been an upvote or answer, I would've deleted the question. I wasn't able to vote for closing since closing as a duplicate with another SE site isn't possible.
How should we deal with such questions (now and in the future)?