This is a good suggestion. This distinguishes between questions or answers that were upvoted long ago, those that are upvoted on a continuing basis, and those that are most significant after some event (e.g. the posting of a better answer). Other distinctions may arise, but these 3 are interesting enough.
I think that this is more relevant for answers than questions. Suppose a question was posed in July 2010, 3 answers were given at that time, and then in July 2011 another answer was provided. The first three answers may have accumulated a lot more votes due to their longevity, but the answer from 7/11 may be upvoted a lot more among the three during the time after its post. This could well be due to a much better, cleaner answer.
Although SO doesn't seem to sort based on current "voting intensity", I believe the proposal is a graphical representation of this idea.