As much as I support this proposal, I agree with @13 that it makes sense to tax the specific behavior that we want to see changed, that is, driving unfettered into Seattle just because somebody can do so.
To wit, I would say that congestion pricing is something to try.
Tax people like a toll for coming *outside* of the city *into* the city during the day when the "price" for doing so is high (congestion, pollution, etc.). Specifically target the revenue for transportation and pedestrian initiatives. Offer rebates for low-income commuters.
Companies wouldn't be "taxed" directly, but smart ones would offer to possibly pick up some or all of the tab for their employees as an incentive to get good employees.
London has been doing it for more than ten years. They even have unexpected support:
"A Republican member of Congress told me last week that he recently was in London for the first time in a long while. 'Traveling was so much better,' he said. 'You can actually get around. That traffic-charging system they’ve got seems to be doing a lot of good.'”
Here's a review of their lessons learned: