Problem is, cannabis is an annual and hops is a perennial.
There's no point in grafting an annual becauseof its short life cycle.
Grafting apple trees is one thing; they live like 50-80 years and take grafts well.
But to play with the THC content of hops you'd have to do REAL genetic engineering, isolating the allele for THC resin production, and inserting it into the Humulus genome- real pain in the ass and expensive to boot.