And probably fatal before you get where that is going. You've got an unusual prize there that won't be hard to peddle for what you think you have in it, and if you take Leo's advice you can style around it without any real strain. Plan your design to hide the straight line and all will be well. Or, put it up for sale. There are two Washingtons and you need to be more specific, there are buyers, everywhere...
The stock most often has a different growth rate than the scion, and therein lies the rub. It is not always so, depending entirely on species/varieties. I have no idea on this one.
Thanks @Forsoothe! I'll very likely leave it be and take yours and others advice who has responded. More of a curiosity of a possible technique.
It's my understanding that bark itself is dead tissue. Without getting down to the cambium, what would kill the tree if this was peeled/cut/thinned down?
It is the outer defense against disease pathogens, etc., bears scratching their itching backs, and guards the vascular system that delivers food produced by the leaves to the roots. Protect it.