As I understand it Brian, and double check this, a chipper must be under 50 hp to skate some of the CARB rules. I had a low hour chipper with the Ford straight six industrial engine that I chose not to do some needed main bearing repairs. To keep it in service would be too much of a liability.
I had heard that in Southern CA the responsible agency has already been following some tree services to job sites and handing out fines to the tune of thousands of dollars.
Even buying brand new, a person may choose to stay under 50 hp because your supposed to keep a log of hours used and where/when running a bigger chipper. Also you pay a yearly fee based on higher hp for that chipper.