And yes, launch demand is an 'economic' factor -- in large part, dictated by vehicle cost (economics of which are mostly technical factors) but relying on the market proving to be elastic, which isn't a certainty.
Let me preface this by proposing that elasticity in the market will come in the form of new business models that use reusable launchers to downsize the size and complexity of the satellites they need. And I don't credit for this idea, it's been talked about and I happen to think it's the way the market will try to go.
However elasticity of the space payload market is going to take a while. No doubt Elon Musk has already done his calculations on this, and luckily for him SpaceX doesn't have to wait years for the market to respond, for two reasons:
1. Musk's goals for Mars require that they perfect reusability, so it's more a matter how how much they can do this while launching payloads that are built and priced for expendable launchers. This period of launching current technology/market-sized payloads on reusable launchers will allow the market to believe that the capability is here to stay, and that they can start designing new business models and hardware to take advantage of it. Hard to say how quick this would happen though...
2. Musk's plan to create a satellite-based broadband internet service using 4,000 micro-satellites. This is the perfect application for reusable launchers, since the risk associated with one payload would be pretty low to the entire system, and they would have more in the pipeline to replace them.
ULA can't take the lead on either of those situations, and since reusability hasn't been proven out yet as practical it would be a big risk for ULA to attempt.
Even more important is that ULA's parents, both of whom make the large satellites that justify expensive expendable launchers today, wouldn't see a lot of value in driving down the cost of launches, especially when that means their satellite manufacturing divisions would be more susceptible to competition from small and mid-sized satellite manufacturers that might see more orders for less costly satellites that can be launched more frequently.
So I think what ULA will end up proposing will walk the line of reducing the price of launching payloads, but without reusability. Plus it will continue to support the idea that large satellites are the right approach, which supports ULA's parents satellite manufacturing businesses.
My $0.02