There's nothing wrong with a good Aussie stock horse for any discipline - they are very much an all round type of horse. I know one who is showing successfully and competing successfully at elementary Dressage as a 6 year old. A friend also took one with not wonderful conformation from Novice to competing Med and training PSG within 3 years. He sold for a pretty penny interstate to a young rider.
This one I would pass on though. The front end isn't as bad as some have made it out to be, but the hind end isn't great. Very much sickle hocked, he will struggle in Dressage at least - I am not knowledgeable on jumping/eventing so will not comment there.
He's got quite a good slope to his shoulder, nice strong, good length of back and is built relatively uphill. Due to lack of muscle development in his haunches, it does appear that he is front heavy. I suspect this is due to him being ridden on the forehand as a result of the sicklehocks.
Keep looking, and certainly don't disregard the aussie stock horses, they're such a great versatile horse!