The Clarity PHEV is available in all 50 States.
Whether dealers choose to order them or not is largely beyond the control of Honda. Oregon is a Section 177 State and has not had any inventory "on the ground" for most of 2019 - a case where demand exceeds supply.
Making it a requirement that there be unsold inventory of xx (units? percentage of all vehicles? at lest one unsold unit in every state every day of the calendar year?) is impractical.
If I were to recommend changes the the Federal Tax Credit, it would become fully available to all income levels and be applied at the time of sale. And PHEV's with less than a minimum AER would not qualify (25 miles?). At this point in time, giving a Tax Credit to a vehicle that cannot reach freeway speed solely on electric power and gets something in the ballpark of 10 miles of range on "electricity plus gas" (from the Monroney label) is questionable. Technology has advanced significantly from when the current rules were written.
But that being said, just getting enough members of Congress to agree on an extension is the major challenge. Getting that same majority to agree to an extension and changing the structure of the Credit would be virtually impossible. Too many would find objection to one or more of any proposed modifications.
Based on some of the other posts here, dealerships can't even order the 2019's unless they're in a CARB state. From your comment they can't order the Clarity PHEV even in CARB states right now, which points to a problem at Honda itself.
The requirement for sales & service in all 50 states can be handled via special orders as long as the dealership will service the vehicle as well. I've special ordered in the past for a hard to get vehicles.
I agree with you on speed - it needs to be a NHTSA/FVMSS general highway use approved motor vehicle. If you want to give partial credits for shorter AER then that's fine, but I'd put the limit at the 50% point for roundtrip commutes.
I like the idea of having the dealership apply for the reimbursement, allowing them to reduce the vehicle price at point of sale. Then take this item off the Form 1040 entirely.
There are two huge public policy goals to be accomplished by electrifying ground transportation. The first is the removal of oil from our national security requirements (the US is actually a net exporter of oil now). Roughly 80 to 90% of all oil usage is in the form of gasoline and diesel fuel. The second is to clean up urban air, which will reduce the long term health care costs related to pulmonary diseases. Just having every one commute on electricity will go a long ways towards this goal.