If you look at what's happening with transmission fluids Power steering fluids,gear lubes and sealed wheel bearings, you can see that synthetic blends and full synthetics are gradually taking over. This is also happening to engine oils, abeit at a much slower rate (mainly due to profit motives by the majors and not product performance).
What you will find over the next 5-10 years is that the least expensive oil you can buy will be a synthetic (Group II/Group III), blend and that most of your high performance engines will mandate the use of synthetic oils, both Group III and PAO. This change has already occurred in Europe, as most of the BITOG listers are aware. It can and will happen in North America, once we go to significantly longer OCI's and vehicle manufacturers have to warranty their engine performance for up to 100k miles...
The total volume of engine oil used in North America has actually gone DOWN slightly, due to longer OCI's. The only growth niche in this market is synlubes, whose market share is expected to triple in the next 5-10 years.
You can take that to the bank....