With the benefit of hindsight I can say a few things about the rise and fall of Keystone XL.
First, about one of the ideas I've written about here that I think has held up best, Infrastructuralism. No lasting gains are going to come about through a carbon tax, trading system, or permit-selling regime. All of these will be subverted as soon as they take effect, if ever. The lasting changes come out when infrastructure is built or not built, because those choices lock in decisions for 30 years.
As Keystone XL illustrates, the major infrastructure-building decisions are never simply made by the magic of the marketplace. They only happen with the active cooperation of government. Even if government somehow absented itself from the decision, there would be no way to build a project like this without governmental use of eminent domain. So the public is already involved in approving or disapproving of all of these projects, no matter how much someone may tell you that they are the result of economic factors beyond our control.
The same goes for the simplistic statements about how commodities have a "global price", as if this just magically happens without extensive publicly supported building projects to make it happen. Without Keystone XL, that oil will have to be shipped by rail and truck, which are more expensive. There is nothing natural about a global price for something that doesn't vary as you cross geographic barriers: it only happens with massive public barrier-removing projects such as the various conflicts fought to keep the Strait of Hormuz open to tankers.
Politically, the story of Keystone XL is a story of -- what is the opposite of leadership? Followership, perhaps. It was always a decision that Obama could make on his own, which was exactly why it was a good issue for 350.org to take up. It dragged on for seven years, and only happened with the combination of a lame-duck President, a change of parties in power in Canada so that we wouldn't deeply offend anyone there, a back-off from the company sponsoring it in the form of their request to suspend, and an upcoming international conference before which Obama wanted some form of face-saving gesture for how little he's done.
What else could have been done with those 7 years? Clearly, the Keystone XL decision has a large symbolic component, and is supposed to lead to increasingly easier decisions to stop infrastructure of this kind. But we can't wait another few years before the next major project is dropped. Making people spend nearly all of the available activist pool in the U.S. on this one project for 7 years was a major cost, one which Obama made us pay with the assistance of supposedly left groups like the AFL-CIO, which supported Keystone XL because of a few jobs. What's going to happen when we have to close down every coal mine? Because that's going to have to happen, sooner than you probably think.