I commented on a Noah Smith tweet a couple days ago, a thread discussing tax policy. AOC (Alexandria Ocasio-Cortez) has gotten notoriety by proposing a tax bracket of $10 million and above with a rate of 70 percent.
I've not followed the debate enough to know what, if anything, she or others have proposed for the current brackets and rates. Personally I'd add more brackets (because "simplicity" isn't important when you use software packages to file your taxes, with increasing rates. And I'd have no problem with the 70 percent proposal.
What I do have problems with is IRS staffing. IMHO the first priority for Democrats is to try to get bipartisan agreement on improving IRS staffing and administration, by which I mean something like doubling the auditors of richer people. One of my early blog posts was to complain about a then-celebrity evading taxes. As an ex-bureaucrat, I want people to follow the rules, damn it.