I would venture to guess that the step up basis upon death may go away
...
While that may be "easy" to do for financial assets, it is EXTREMELY difficult to do for almost all other assets. It might cause all sorts of unexpected issues if implemented. And in some cases, it would cause issues even with financial assets.

I'm not sure I follow. Pretty much every other jurisdiction with inheritance tax has no step-up basis rule, and things tick along. I presume an estate files a final-year tax return for the year of death anyway, and the valuation of every asset has to be done either way. No matter, it's not my worry.

Side note on the whole general subject:

Nobody likes estate taxes, as a rule. There is an atavistic desire to pass one's assets to one's children. On the other side, most people are sensibly a little uncomfortable with the idea of dynastic wealth: if one great-great-grandparent made a killing, every descendent is set for life for generations to come, so society has a permanent over-class plutocracy.

If appointed emperor of the planet, I would propose a compromise: no inheritance tax passing things to your spouse or kids. But it ends there: gifts and bequests fully taxable (probably at a high rate) arriving in the hands of anyone else, and if you pass along wealth to your kids, whatever amount that YOU received during your life as tax-free inheritances from your folks, adjusted upwards for inflation, is (heavily) taxable arriving in your kids' hands. So the tax loophole is once-and-done on any given block of money. A family can remain wealthy generation after generation, but only if each generation adds meaningfully to the pile through their own endeavours, not just collecting economic rents. A generation or two of coasters puts the family back into the herd to fend for themselves.

Jim