Brad,
Yes, if your idea is to irrigate 80-90% of your golf course in a conventional manner, then you are not going to change much.
And I'm not arguing that.
But I am telling you that if a course used SDI on a more wide spread approach, the savings in pump, pipe and other irrigation components are huge. Yes, it is doubtful we will see much SDI in the mid west where water is abundant and cheap. Right now, SDI costs significantly more to install then a high end irrigation system. Where a high end over head system with most of the modern bells and whistles might cost 2M to irrigate a 90 acre country club, SDI would cost ~2.7M - 3.5M. So in areas where you don't have to save water, it's use will be minimal, not only due to cost but also due to acceptance.
But in areas where water costs are $1000/acre foot and annual water bills run into the 400-700K range, or where water is very limited and in short supply, saving 50% of your water starts to look a whole lot more appealing.
All you have to do is look a little harder at the technology and spend some time researching and I think you'd start to see why it is worth considering. You talk about single head control (and every system i design has single head control), but optimum control is regulating water in the ROOTZONE, not on the surface. Start doing your water audits based on soil moisture and not catch cans, and you'll quickly learn the assumption of perfect uniformity on the surface = perfect uniformity in the soil is a complete myth. But what better way to achieve optimum soil moisture management then to deliver water directly to the area it is needed. Combine that with good sensor technology and you are managing irrigation at an entirely different level.
Irrigation reservoir? Why? You are no longer needing to push out hundreds of thousands of gallons in a short time frame as with SDI you can irrigate anytime you want, and because the flows are low and you are using half as much water, at much lower pressure, the traditional reservoir pump station model is replaced by a closed system with everything sized to work with your water source. Its a closed system and the water never sees the light of day. Sound like fantasy? I believe you will see that exact system with in five years. It will not be in the mid west, but maybe in AZ, NM, CA, UT, AUS, or the middle east. Areas like that are already switching thousands of acres of vineyards, orchards, and other perennial crops over to SDI, and I'm not talking about old drip with an spaghetti tube sticking out of the ground next to the plant. I'm talking about closed systems with emitters built within buried tubing where there is zero evaporation, run off, or wind loss and all the nutrients are delivered with the SDI as well.
Lots of people, like Dr Leinauer at NMSU are working on that goal, and it is being tested and used all around the world. I've received a PM regarding a researcher who is using SDI on greens in France and I will be reaching out to him. Why in France? Because in some parts of France you can not drill a well and you have to use rain water capture to have any water to irrigate your golf turf. You live with constraints like that and you find real ways to conserve water and still grow good golf turf.