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.
2018 Clarity Electric (Vortex Blue)