The idea behind these rules was to reduce the fees paid by merchants, perhaps with the hope that this savings would be passed on to consumers. This is a fantasy, similar rules are in place in Australia - with no effect on prices. Current fees are in the 2-3% range, plus a fixed fee of 15-25 cents. This means something that costs $9.99 has a fee of around 35 cents. Do you really think the retailer will cut the price to $9.64? This might have an effect on certain high financial items, like insurance, and it might mean that some companies that previously rejected cards will allow debit cards, but it will not have an effect on prices.

Increasing checking account fees are already a reality. All of the major banks are increasing fees and/or requirements to have an account. This will naturally mean some people close their accounts entirely, opting instead to rely on "no checking account" services. This will ultimately mean more money for those who prey on low-income individuals, and fewer people able to participate in the online marketplace.

As these rules start to go in effect, retailers will start to make customers aware of the differences between their cards. Signs advertising which card brands are accepted could be replaced with which banks are accepted (only those larger than $10 billion and thus subject to the 12 cent cap). There are 74 banks that are subject to the cap, so a more likely scenario is that those banks or networks apply a logo to their cards which guarantees the fee is 12 cents or less. In any case, customers of smaller banks will find that their cards are not accepted. Likewise, credit card acceptance will drop since fees on those have not changed. Customers will be expected to know which debit card networks their card supports ("Sorry, we only accept Visa cards with a Plus logo"). 

Note: While 74 banks have more than $10 billion in U.S. deposits, it's unlikely that all of them issue debit cards. 

So, the net effect could be that consumers are forced to get accounts at large banks, many of which will charge fees in order to hold an account. Small banks will be forced to either match the 12 cent cap, or see their cards rejected by retailers.

While checking account and debit card revenues drop, credit cards have been virtually untouched. They still have the same interchange fees, with the added bonus that customers with poor money management skills will generate enormous interest revenue. Chase is already running programs to encourage checking account customers to open credit cards, and vise-versa. I wouldn't be surprised if we start seeing banks issue ATM cards that are actually credit cards for purchases. That is, when you swipe the card at a retailer or use it online, it's a credit card, but if you use it at an ATM it accesses your checking account. 

On the plus side, in trying to drum up credit card business, banks might improve their rewards programs.

Online banks have a huge advantage when it comes to costs. Personally, I keep my money in an Ally Money Market account. I get free checks, free ATM access (they re-imburse any fees you are charged by the ATM owner) and 1.09% interest. For the rare instance that I have a real check, they provide free postage-paid envelopes to send them in. There are no hold times for customer service, just call the number, press zero (it tells you to, the other option is the automated banking system), and a person picks up very quickly. I keep my transactions at less than 6 per month by using a credit card for normal purchases (paid off at the end of the month). They also have a checking account that pays .5% interest if you don't want the 6 transaction limit.

Ally will be subject to the 12 cent cap, but there's little indication that they're dependent on interchange fees. They also don't have an overdraft "protection" program. Instead, they might allow POS/ATM overdraft without a fee at their discretion. For checks and automated payments, an overdraft will trigger a $9 fee, but that can only be charged once per day, and only if you will overdraft by $10 or more. I have never actually overdrawn my Ally account, but I think that policy is a good demonstration of how they do business.