Before that day comes...you will be famous doing the show circuit; teaching, doing demo, etc. already
Unless you just purchased a great tree (close to 1mil already) and flip it.
In order to sell a tree for 1 mil, IMO the following would have to occur:
1. I would have to collect it or grow it from seed, cutting or air layer-this would take the majority of the rest of my life- i'm 29 right now
2. I would have to find an extremely wealthy client that could not live without it and connect with him
3. Bonsai would have to grow by leaps and bounds in the U.S. which would get more people involved and more wealthy people involved
4. High level competition would have to increase in the US, which would drive both the quality and price of trees up in the U.S. Kokufu/Sakufu status in the U.S.