Lawrence Zelenak (Duke; Google Scholar) presents two papers on Income Taxation of the Unrealized Gains of the Ultrarich: The 1920s, Stanley Surrey’s Era, and Today at Northwestern today as part of its Advanced Topics in Taxation Colloquium hosted by Gregg Polsky:

1924, 2021: Taxes of the Ultrarich, and Mark-to-Market Reforms, 172 Tax Notes Fed. 583 (July 26, 2021):

In this article, Zelenak tells the story of Treasury’s disclosures of the income tax payments of plutocrats almost a century ago, which mirror the recent ProPublica revelations of the income tax payments of the 25 richest Americans, and he explores why those earlier disclosures — unlike the recent ones — didn’t spark interest in mark-to-market taxation of the ultrarich.

Stanley Surrey and Taxing Unrealized Appreciation, 87 Law & Contemp. Probs. __ (2024): 

Decades ago Surrey presciently anticipated this sort of evolution in the views of the public and of members of Congress toward the taxation of unrealized appreciation. Presented with today’s attitudes he surely would have supported inclusion of nontaxation of unrealized appreciation in the tax expenditure budget, and very likely would have supported the Wyden and Treasury billionaires tax proposals as well. As Surrey noted in the above-quoted excerpt from Pathways, he could have pushed in 1973 for inclusion of the nontaxation of unrealized appreciation in the tax expenditure budget, but if he was right (as I suspect he was) that public and legislative opinion on the topic was then still mired in stage one, it is hard to see what that would have accomplished. And although Surrey sometimes took on battles he did not win (more on that below, with respect to the tax-free step-up in basis at death), he was never interested in fighting battles he knew he could not win. It is probably ahistorical to think Surrey should have done anything more than he did with respect to the realization-based character of the income tax.