While I want Rupp to stay focused on the 10k, I actually agree that he'd be better off trying the 10k/marathon double at the Olympics than that 10k/5k. The 10k is a one and done event. He then has the whole Olympics to rest for the marathon that will be run at a slower pace than his 10k. If he does the 5k not only does he have to run an additional round, but he'll have to run faster on likely tired legs.
Realistically he could enter the 10k/5k/marathon triple and actually qualify for all three given how the trials are done. In this modern day (unless USA track continues to decline) I think that would be a huge contribution toward his legacy more than another silver or a bronze in anything might be.