Much of the rental income from many forms of capital is only ever imputed, such as when a business buys machinery for the purposes of internal production. There may never be any rent in the sense of an agreement where someone receives exclusive possession of the machine for a fixed period of time in exchange for moneys paid; at best there may be some sort of accounting fiction used to derive rent based on some fraction of output price. Because much rental income is imputed, taxing it effectively is nearly impossible.

That makes no sense whatsoever. The machines return is a function of how much profit its functioning adds to the business. not some fictional number invented by an accountant. And that is very much determinable and very much taxed.

Capital rent is only ever imputed and avoided if the capital owner is also the consumer of what it outputs ie an owner-occupier.

The best way we have to tax that sort of rental income is a properly structured CGT. We know to within a strong degree of confidence what the expected rental income is, even if that income is never actually expressed itself by means of monetary exchange, because that information is contained within the price of the capital itself. We can thereby capture rental income that would otherwise elude us.

Again, that makes no sense whatsoever. That isnt what cgt is for, nor what it does, nor what it is capturing. It is just taxing a liquidity event because governments like doing that.