There is no state income tax . . . yet. But the "soak the rich" band is already tuning up, and with the cost of living being what it is out here, "rich" will probably include anyone who can afford a house.
https://ballotpedia.org/Washington_Initiative_2111,_Prohibit...
Especially in a future where young, productive people are going to be in shorter and shorter supply.
I agree with the sibling comment that this is not something to realistically worry about at all.
The WA state constitution says non uniform property taxes are not allowed, and 1930 WA Supreme Court ruled income was property.
A flat income tax would have been allowed, until last year when income tax was outlawed, but not with enough votes to amend the state constitution.