Earlier quoted context omitted.
It's a good point. At any given time, the key is either compromised or it's not. And you may or may not know either way. If it's compromised, and you know, then it should be revoked -- if your only mechanism to revoke it is waiting some amount of time (several days, months, or even a decade) you have a pretty big problem. If you don't have a way to detect if it's compromised, rotating a precaution almost makes sense…
I'd say sign the next root certificate with previous root key, then you can rotate root key automatically. Browser update works the same way: you download new browser with new root certificate authenticated by previous root key.
Most roots are required to be cross-signed today by all the major browser and OS vendors. What you have is a classic web of trust issue because it's the new key that has the signatures attached so you could take the new key/certificate at its word, but if the problem is the previous root expiring, how do you trust that the new root certificate was signed by the previous root before it expired? You can't trust the now expired root can you? If you restrict it to the subset of time where both roots are unexpired, you have the exact same problem as the intermediate game that the BBC has to play in the article.