I like this question, although I don't think it could work. Someone who campaigns really well, does not necessarily mean they will fulfill their office well. It also penalizes when there are two good candidates running against each other.

I could see it being more viable if the upper term limit is still along the lines of what we have today. Perhaps a presidential candidate winning an election by landslide could get a maximum term of 8 years, whereas someone just barely winning would have a shortened term of 1-2 years. I would definitely still be concerned about the negative ramifications of potentially more and more dirty campaigning to try and capture the highest portion of votes that others have mentioned.