Yep. That isn't about publicly traded companies. The only people that would panic is if you are in a startup that cannot exercise.

Yeah, mostly applies to pre-IPO companies offering stock options/RSU's.

Large publicly-traded companies can also offer RSUs---doesn't this still apply in that scenario?

In practice, RSUs already work that way: you're taxed on RSU delivery, which in the case of a public company is almost always the same as the vest date. Usually the company will sell a portion of the RSUs vested to do tax withholding on the spot, and then you're immediately free to hold or sell the remainder.

I the case of a private company, RSU vesting/delivery means you owe taxes but (usually) can't sell them to pay for it, which is (also) no different from today.

I'm under the belief that vest for tax purposes isn't until the share becomes liquid. If the startup can't exercise then, for tax purposes, has the share vested? I believe it has not (and have, in the past, filed taxes on this belief, with the support of my accountant.)

You're describing how things are now and have missed the point - this bill will mean that you will have to pay tax on vesting.

Am I? I thought I was providing supporting evidence for the adjustment of when "vest" actually occurs.

That's not supporting evidence; your believe is incorrect. Vesting is unrelated to liquidity and can occur without the ability to sell shares.