Both arguing the same points at the same time is quite the Baader–Meinhof coincidence.
Upper middle class its where highest quality of life happens, if one is smart enough to understand how happiness and life fulfillment works, to not die full of hard regrets. You can have meaningful true friendships. Enough to afford whatever is you need or desire to do, not enough to become self-entitled spoiled lazy disconnected from reality piece of shit parent and partner type of folks. No you don't need private jet or mega yacht or 5 mil hypercar for that, that's poor man's idea of what sort of quality wealth brings you in life.
EDIT: I’ve misunderstood your comment, I don’t have any alternative accounts on hacker news!
A perfect tax code would be impossible, a more simply one would be very doable.
We're talking about a campaign proposal here with no legislative draft so its a guessing game, but in my opinion any move similar to taxing unrealized gains will serve only to make it more complex and would not fall under the category of "good" for me.