Lots of states are going to be a problem, Oregon, Washington, (obviously Cali) and many other no longer have the easy plating they used to.
I have lots of friends here in Oregon that have a plate, but the DMV will not renew their tags once they expire. Basically Oregon's stance is if the VIN # isn't approved by DOT for highway use from the factory, no dice.
I expect most of the Nation to be this way at some point.
But if you want to go for a new bike and spend lots of $, KTM is the best option. You might be tempted by the DRZ400s (street legal), but it is significantly different from the now discontinued DRZ400e/k (dirt version). It is heavier and slower. Many people have purchased a DRZ400s and converted all the parts to make it like a 400e, but you are talking about a lot of money, (carb, head gasket, exhaust, cam) instead just go buy a KTM.