I thought about this too. Then you have to deal with two game saves. To many issues I think. The solution is to keep the servers running and perhaps have a secondary back up servers located at a different location like big companies do.
There will be only one save.
The save on your local HDD would be the same as this one on the servers.
Your local save will be updated regularly and uploaded to the servers if the connection is working, or uploaded to the servers after the connection comes because of a failure.
So, you have to deal with only one save, not two!
Now - as it is, you have no local save at all.
Everything relies on the save that's on the servers.
That means, you can save your game progress if the servers are running and not at all if the servers are down for any reason.
That obsoletes the reason to play GT sport, as your progress will not count the next time you start the game and the servers are down again.
I mean, what's the reason to play if you lose all your money, mileage points or even gifted cars, if everything will be gone if you restart the game after one hour and online save doesn't work again.