Or maybe....keep as is....Keep top pruned back hard, use one sacrifice branch and plant it out in the ground and grow it out for 5 years and let the trunk catch up to the top.
That's probably the best option, but you will want to be
very proactive in cutting the top back over each growing season in hopes of promoting some sprouts on that long, thin trunk.
The tree was propagated with a "yard" in mind. Meaning it was allowed to grow very straight and tallish keeping the first branches rubbed off until it looked more like a yard tree. A bad component of bonsai.
Which is why "regular" nurseries are difficult places to find material that can some day become a decent bonsai -- especially if you are shopping for a
tree as opposed to a shrub. The commercial growing practices for future bonsai are
radically different than those for landscape use.
You should never enter a neighborhood nursery thinking that "I WILL find a tree today. Chances are -- even after looking at every tree on the lot -- you won't. And if you don't find one that screams BONSAI at you, leave it there.
Or buy a shrub -- a juniper, crape myrtle, cotoneaster, holly, azalea, etc. You are much more likely to find one of those with a single, short trunk that can become a bonsai in a relatively short time.
In all my years in bonsai, I can remember very few decent Japanese maple bonsai that started out as a landscape plant, and the ones I do recall, were bought when they were very small (1-3 gallon size) and grown into a bonsai, not chopped down from a tall, leggy thing.