That answer is that the winner of a penalty should be the one to take the penalty.
It is important to note that I am not the originator nor the only person to have thought of a great idea.
As things currently stand, anyone can take a penalty regardless of who won it. That rule is okay, there is nothing wrong with it, but if the goal is to make the game a little more entertaining, then the answer is not to clear new rules out of thin air. The answer is to enact a minor tweak that increases the chaos and entertainment of the sport. Imagine the added chaos if a center-back who hasn't taken a penalty kick or scored a goal in five years somehow wins a pk with 5 minutes to go down by 1 in a knockout game? Penalty kicks already generate a lot of excitement and nervousness, a rule change like this would only increase that valuable commodity.
But I'll be honest since you're friendly enough to have read this far into the article. The real reason FIFA should enact this new penalty rule is what it'll do in ending unnecessary sports debates on whether a player is a penalty merchant or a truly quality goal scorer.
Thanks to social media, the last decade has seen sports talk devolve into meme debates about who the best players are and, when it comes to goal scorers, the idea that some are nothing more than good penalty takers. It could be a tweet about a U19 player in Germany signing a new contract, and if it picks up enough traffic, then you're guaranteed to see a response with something like, "Penaldo is overrated" or "Pessi would be nowhere without penalties."