There may be some inverse taper in the trunk but it is possible to transplant larger JM.
You can get away with remarkably little root when transplanting maples. I generally chop roots back to around 1 trunk diameter when transplanting maples.
Japanese maples are unpredictable when doing drastic chops. Sometimes they come through with all roots and branches alive and well. Sometimes one side will die off completely for no real reason. All you can do is try.
As to whether it is worth, depends on your skill level, what other trees you already have and how much you value your time, effort and potting soil.
My observations after many years of collecting:
Trees look great in the ground. Not quite as good after it comes out of the ground. Worse when it is in a pot. After a few weeks you'll wonder why you bothered.
Trunks are much bigger once you get the out of the ground. make sure you have larger containers to put it in.
Trunks weigh way more than you imagined. If you plan to retain soil on the roots plan to have a machine or some good friends with more muscle than brains to assist. ( no beer until after the job is finished!)
The bonsai pot you will eventually need will be bigger and cost way more than you imagined.
By the time the tree is showable you'll be too old and decrepit to move it, especially if you insist on digging more big trees.
have fun whatever you decide to do with this one.