Well, first off, the tree is far from mature. If your wife is unhappy with how it looks now it seems silly to remove a landscaping tree if that's what you want in that area. You can prune it to shape and use guy wires and stakes to pull it into position. You could even easily remove one of the trunks to get a single trunk landscaping tree.
As for growth... it is my understanding that container plants may show superior growth for a year or two. This is because the root system is contained so energy is spent above ground. Eventually all growth is stunted. When you plant something in the ground the majority of initial growth is actually underground while the plant establishes a good root system. After a few years when the roots are developed top growth really takes off and quickly surpasses anything grown in a pot.
Now for bonsai there is always potential if you want to try. Do you know what cultivar it is? I have a large JM Bloodgod in the front yard of my house. That cultivar is a poor bonsai specimen because it has rather long internodes. But the bigger the finished bonsai tree is the less this matters. It would be best to collect a year from now and go around the base of the tree 18" out from the trunk driving a spade into the ground to sever all horizontal roots. If you can't do this keep as much of the root ball in tact as possible when collecting. Either way you can chop off the top growth, maybe 6-12" above the "Y". If you successfully collect it I would air layer right below the trunk split for a mother/daughter tree (although it will take work to make one trunk more dominant than the other) and the base can be used for an informal or formal upright. That would give you at least two trees to play with. If it's going to the trash there's no harm in trying.
