It would be worth the last buying price for that owner, that is $44 billion. Gives an incentive to negotiate down as much as possible, instead of buying at inflated prices. The seller pays capital gains and the buyer pays a wealth tax on the asset.
It doesn't matter if Twitter is a negative income entity, if it is ascribed some value. It would essentially become the equivalent of a white elephant. There used to be a time in India when people who did not have an income but had lots of erstwhile assets (usually upper caste folks with zero skills) would sell off their properties just so they didn't have to pay wealth tax. That was essentially how my parents bought their first property.
The caveat is that enforcement is going to be a bitch, black money will proliferate in the market but if digitally maintained, collection could be streamlined.
I don't doubt that it's an accounting nightmare, but Elon Musk can afford an accountant who can apply the Generally Accepted Accounting Practices.
I have no doubt that games would be played, and that the IRS would constantly play cat-and-mouse with them. Arguably, we could solve the problem without a wealth tax just by funding the IRS properly to enforce the rules already on the books.
That's why things like this happen. Rules get written; wealthy people subvert them; new rules pile on more. It's not great, but it's better than the alternative of just giving up.
I actually have no idea whether a wealth tax is a net benefit. I just know that it's not going to happen in my lifetime (not with a Supreme Court guaranteed to find it unconstitutional), so I don't spend any time thinking about it on the merits.
I'd say a start would be what is the value it's being borrowed against? Quite often you see rich people getting loans based on the imaginary value of these ethereal assets. Seems like a good starting point for taxation.
There is this doctrine
https://en.wikipedia.org/wiki/Georgism
which tends to push people towards more dependency on property tax, particularly the idea that high property taxes might be a good thing if they drove people in San Francisco to abandon their single family houses. I posted an article from Jacobin advocating that a few weeks back and was shocked to get a swell of people blaming immigrants for high rent that and some other experiences make me wonder if YOShInOn and I should quit posting articles from Jacobin.
(That said, the left around Ithaca NY has gotten the idea that high property taxes cause high rents but that's because Ithaca has the unusual problem that so much of the land in Ithaca belongs to educational and other institutions that are tax exempt so the remaining landowners have quite the burden.)
If someone has some income they can sock some of it away to pay the IRS. If you look at the case of Twitter, for instance, how do you tax it? Is it worth $44 billion, $22 billion or is it a Superfund site that has negative value? How does the owner get the cash?
(I think of how the business model of Premier League football seems to be something like: buy a team for $300M, lose $30M a year running it for ten years, sell it to someone else for $1B, at least you can tax a $700M capital gain - $300M of operating losses.)
The manipulations that people can make with capital gains are already bad enough but when you sell something there is a real price, there will be all kinds of crazy games with a wealth tax.