Some of us at Plug In America (not me yet) have been talking to WA legislators about extending the sales tax waiver. It clearly sells more cars, it doesn't require appropriations, it helps WA meet clean air, clean water and CO2 goals, and it is a HUGE boost to the economy to have car owners buy local electricity (and keep lots of money for discretionary spending) instead of out-of-state petroleum. It's high on the Seattle EVA's legislative list as well, and CATES (who is also working to get some health-related orgs on board). Jeff Finn created a chart calculating costs and savings, and it's clearly a good investment for the state - more so for WA than most other states.
However, even legislators that own EVs and are very receptive to these arguments are still worried about getting this extended. The big problem is that they have the education funding sword over their heads, and they are in a mood to cut anything they can. Something like this that doesn't even need cutting, just non-renewal, is at very high risk. If it does get renewed, it will likely have a $50k cap (that is, the waiver will only apply to the first $50k of the sales price).
Of course, that's short-term thinking...short-term revenues might rise slightly due to extra sales tax revenue, but having more car buyers send money out-of-state for petroleum is going to hurt revenues in the long run. Still, most legislators aren't much better than consumers on short-vs-long tradeoffs; they figure they will be out of office by then anyway. Sigh.
If you want to help, join a group like Plug In America, Seattle EV Association, or Six's WA EV PAC. And write your legislators. There may be coordinated actions in the future, so watch this space.