I don't see any issue with JetBlue adding a basic economy product. From what I have heard, the tvs aren't going anywhere, the leg room will still be among the best in the sky for domestic carriers and the snacks still unlimited. Also, they do not plan to charge for carry on baggage so you can still bring your backpack/briefcase to put in front of you in addition to a bag that fits into the overhead space. The real question to me is will basic economy purchasers get to select seats. If so, what exactly are they taking away?
I'd guess the tickets will be non-refundable and non-changeable. You board the plan last. No seat selection. Limited or no JetBlue points can be accumulated.
What's interesting is that a new trend with the US carriers will be to charge for seats near the front of the cabin. Nothing different about the seats - no additional leg room, not special food and/or drink options, nothing. Just the fact that you're sitting at or near the front of the cabin.