How could it be otherwise?registering the boat in another state
looking at it as an option to buy me some time to either involve some legal types (if needed) or see if I can transfer an out-of-state registered "homemade" boat to Pennsylvania
An out of state boat must be registered, they require that.
You think they are going to say "this boat is banned from PA waters"?
I think that would require some very solid rationale of the public interest involved to stand constitutionally.
Generally a vehicle accepted as registered in one state, gets accepted when the owners moves to another.
Sure maybe tighter inspection, pollution / safety regs, but can't just irrationally ban a very commonly accepted type of boat completely.