Credit cards won't go away. People want digital payments, they don't want to always carry cash. That's a large part of where payments have evolved to. You want to turn it to ACH / Debit as a way to sidestep CC companies. You somehow don't think CC companies should actually make money. CC companies make money in two ways: from merchant fees and from interest on unpaid balances. They also take risk on the issuing of credit and the potential default on balances which we know happens every day.
Another reason CC cards won't go away is that people like to spend money they don't have yet, and might not have for some time. ACH and Debit requires you to have the funds. In the U.S., we are increasingly a nation of debt. iPhone, Xbox, PS4, etc. Ring it up today, pay for it ....when?
It is possible that over time Apple could partner with banks to expand Apple Pay to use Debit cards. However, this would be far more likely for larger institutions like Wells Fargo, Bank of America, as your local regional bank where you have a checking account and Debit card are probably not going to be as easily able to sign up for Apple Pay Debit or as easily motivated to do so.