No update on this little guy, winter bit him. I did go ahead and start another but not in a mame pot, just a cheap shohin pot my fiance got me. It's done well so far, I'll see how this one winters over. (This time they go in my tree house AND get mulched in lol.
When you have hundreds of trees in development, it doesn't hurt to experiment. I'll be developing this mimosa, a silver maple, vitex, and eastern redbud all in bonsai pots for their lifespan. This time I'll offer my little ones a bit more protection over winter.