I can't think of anything worse than somebody who works for 40 years, saves a ton of money for retirement, does everything right to live the Good Life only to have the feds say, gimme more.

Sure. We don't want to target someone like that. If he worked 40 years, paid his taxes all that time (assuming a reasonable variable rate based on income), he shouldn't get whacked. Likely your worker will have lower income, and pay less tax on dividends and capital gains, so that's fine. That's pretty much the situation I'm in now (except I only worked for ~30 years).

So how about this: A micro transaction tax on all stock trades where the asset has not been held over X period of time?

OK. Maybe less than a week? I knew a "day trader" (he worked at my company as his day job), and he said you wanted to be out of a position by the end of the day. So he would start buying when the market opened, and would be sold out of everything by market close. Though I don't really see why we don't just tax that as ordinary income. All stock gains, all dividends. Just tally it up with any salaries, stock plans (a lot of big-wigs get paid in stock), etc, and tax it at an appropriate progressive rate.

And when the Gateses die, their kids should have to pay tax on the value of the estate. A lot of wealth gets handed-down tax-free because it's never actually liquidated to "realize" any gains. Exceptions made for smaller estates (e.g. family farms, probably you and me and everyone posting here, etc).

Just hand-wavy. Details would need to be hammered out, obviously. But, unfortunately, our system assures that Congress is in the pockets of those uber-wealthy (bribes...errr..."campaign contributions"), and the wealthy wouldn't like taxes touching them. As one of them once said, "only little people pay taxes". And she was right, the wealthy have fixed the system so that is mostly true.