I can't see them raising the $200 NFA tax stamp. I could see Congress at some point in the distant future, repealing the Hughes amendment in exchange for a $3000 machine gun tax as a condition.
Let's face it. The US government does not want it's citizens to have access to affordable machine guns.
In the old days most chief LEOs would just say no and that would be the end of it. Revocable Living Trusts were not held as legal under the GCA of 68 until a court case in 99 or 2000.