Just wanted to highlight that the ruling is in, and the State Supreme Court has, essentially, said it's constitutional. 

https://www.courts.wa.gov/opinions/pdf/1007698.pdf 

As a stopgap measure, it would be really nice to have a diagnostic that catches when a client is a Washington resident with long-term capital gain over $250K. Lacerte did something similar when the American Rescue Plan changed the rules for unemployment benefits halfway through tax season.