Whether it is a million or two million is immaterial for the discussion below, but I think success means the price of bitcoin will be quite a bit higher than that. Transaction fees were reduced again by a factor of ten as a means to encourage microtransactions. Delivery, in this context, simply means exchanging the financial instrument for cash. It also isn’t a problem with physical cash because you can’t hand two people the same single dollar bill. Note that this only affects people using the new sighash flag; it doesn’t affect unrelated transactions. In fact it is not only Postel’s Law that predicts this, https://youtu.be/mXxejqmTyqw but also greed-because miners make money (bitcoins) by adding transactions to the bitcoin log, and never mind where those transactions come from.