I've just read the FED's speech on interchange fees. Most striking, in my view, was the conclusion that this is a complex issue. Now, the FED are good thinkers, and if they say something is complex, it means that even they can't make something out of it. So if I read the text below with that in mind:
In light of the novelty and unusual complexity of the issues raised in this rulemaking effort, my colleagues and I are very interested in reviewing the full range of comments offered on our proposed rule and are reserving judgment on the terms of the final rule until we have the opportunity to benefit from these comments.
This just looks as if the FED are saying: Sorry, but even we don't know what to do here. So my guess would be that they go for an easy, less controversial solution. Because in the meantime, I noticed in the SEC filings that Visa and Mastercard are already preparing for a large legal battle (and have agreed how to share the burden between them). And from the above, I reckon the FED is not looking forward to more complexit or novelty.