I'm not a WA resident so I can't speak about what is or is not "street legal" there.
As noted, if 2A supporters or gunners feel they need new gun laws to get these items(class III guns, AOWs, SBRs, surpressors, etc) then have at it.
If current laws or statues prevent these firearms or weapons and new bills change it, then it's good.
My point is that if these new gun laws go into effect in WA, I highly doubt the gun shops & FFL holders will be swamped with new orders/sales for SBRs.
Outside of a few cops, armed professionals(EP agents, PIs, bail agents, PSCs, etc), collectors, and weapon-tactical instructors I doubt many WA residents will even purchase the SBRs.