Article I, Section 9, Clause 4 of the U.S. Constitution would like a word (assuming you’re contemplating a federal wealth tax; states could do it, at the risk expressed in the headline of the article we’re discussing).
That is what makes the timeline GGP laid out impossible:
> We can pass a wealth tax tomorrow and it’ll suddenly be taxable.
Unless we don’t share a common definition of “tomorrow” or “suddenly”. (For reference, the 16th Amendment process took about 3 years and 7½ months from Senator Norris Brown’s initial formal proposal to ratification by the then-necessary 36th state. [You would need 38 states today.])
The point is that we can do it if we want to.
When you meant "shortly before Memorial Day of 2030", it's not clear that 51% of the misunderstanding is on the reader.