Sema is still heavily involved in influencing automotive registration and such, but there's only so much they can do. They have been lobbying the American Association of Motor Vehicle Administrators (Those people who manage your state DMVs) as well as state legislators and THERE is where things break down. If a state law-maker is also influenced by a special interest group (or even an individual with deep pockets) all of the best intentions of SEMA can be thrown out in a bill that might have been beneficial, even helpful. Trust me, I've seen this.
There has been a strong effort to move states in the direction of consistency of terminology and vehicle classes between states, especially in terminology of different types of vehicles. Lots of different names for the same things between states used to exist, but now are becoming the same between states (with some notable state hold-outs). As Tip O'Neil once said, "All government eventually is local" and the states will continue to have their differences, based on local influences.
For example, I never knew what a "Glider" truck was until I got involved in Massachusetts legislation, only to find that people were ordering new Semi-Tractor "kits" without current engines to have older, refurbished diesels installed so the operator could avoid current emission regulations, get better fuel mileage and save money (even though they polluted more). The largest Glider producer (Fitzgerald) was a big contributor to the Trump campaign, but the states are moving in the direction of stopping the Glider practice by the end of 2021 except for California which still allows them, but the engines must be 2010 or later. Many more state loopholes exist (good and bad) for these and many other vehicles.