Riding vs Racing
If he likes to race but doesn't want the ........ which comes with an international racing series, why not just by a bike and join a racing club in Australia? The interest on his career earnings alone would probably pay for a few seasons of club racing.
I wonder how much he really liked
racing as opposed to riding.
I always got the sense that he preferred the qualifying rounds to race day. Sure its great to be first across the finish line, proving yourself the best among the best in the world, but the path there was more 'work' than 'play'. (I get a hint of the same from Lorenzo.)
Meanwhile Rossi & Marquez come off as guys who
live to race. Live for the battle. For whom the best part about the race isn't finding the fastest line around the circuit but overtaking the guy in front. Sure Rossi's mellowed quite a bit now, with age and two humbling seasons at Ducati taking their toll, but in his prime he was a rider who'd rather battle someone to second place than finish a lonely first (that was his team's impression at least).
Same with Marquez. After blowing his championship hopes in 2015, he's tempered his approach, but its taken a constant and very conscious effort on his part. You can see the struggle within as he fights the instinct to cut loose. Unsuccessfully at times (case-in-point: Silverstone).
Sure both of them can ride responsibly if the situation calls for it and Stoner proved he could battle as hard as the next guy, but it doesn't seem to be their 'natural' state/mentality.
So I think I can see why Stoner would be willing to retire at his prime, stick to testing and fight off the temptation to return. He doesn't live and breath racing. (Marquez, in contrast, will be flogging his bike to beat younger riders even after the reflexes of youth fade. Rossi will certainly pass away.. of old age.. on the track.. on his bike.)