Especially, when you can improve all 3 of those situations by simply generating a new address for EVERY transaction? A business wouldn't re-use an invoice number, why would you re-use a bitcoin address?
I don't want to diss you but are you from another planet?
The invoice number? A Bitcoin address is more like a customer ID, which remains fixed!
It would be much more convenient for businesses or individuals, to provide their counterparties with fixed addresses for further use.
Otherwise a new one would have to be created everytime someone sends you a payment. What a nuisance! And imagine this is done automatically, and a partial payment is received: CHAOS, CONFUSION and MAYHEM!
For privacy you would need a new private key (HD) every time anyways. But if you want privacy, BTC is not the right crypto.
I guess a company with good blockchain knowledge could try and create 1 private key per customer, then issuing a different address on that key for each invoice. But for the average company/individual that is way too much overhead.
So yes I do think address re-use should be fully supported.