I have to ask, are we really at the end of the Second Golden Age? Seems to me the designers we most associate with this second age, Bill Coore, Tom Doak, David McLay Kidd, and now I suppose, given his work at Kinloch and Ballyhack, Lester George, are all fairly young men. Given the rough average age of these guys, roughly 50, we have 30+ years more of these guys designing courses if they design into their 70's and 80's like Pete Dye and Robert Trent Jones. Seems to me that we might be just in the middle of this Second Golden Age.
I posted that on the thread about Ballyhack in response to Ran saying that the Second Golden Age might be nearing an end. I think it might just be getting started.
In 20 years, I think we might be seeing courses with less maintained space, with extensive waste areas like seen at Pine Valley and others; that trend is all ready going, but it is likely to get bigger.
I think the courses will generally look the same as they do now, though I think you will see them on sites that are more extreme than before due to the modern ease of getting people to those sites and the relative ease of building on them.
New grasses will likely be a big factor, grasses that can maintain an emerald green color, to satisfy the American country club golfer, while getting 50% or less water than current grasses, I am sure are being researched quite a bit right now. Also grasses that allow a faster and more survivable putting surface.
Certainly I think that at some point in time we will go back into another dark age. The European Renaissance didn't last forever, neither will this period of golf architecture. However, same as with the Renaissance, much of what we learn and do during this time will be passed down and expanded upon. Although, perhaps rather than going into a true dark age, perhaps we will just move into a period where you see a slight slow down in new, original ideas.