With all these posts lately regarding Google and search it does appear that the off-site SEO landscape will change dramatically very soon. You have to ask yourself is investing in domains names a worthwhile proposition anymore or would your money be better spent in the stock market.
I already invest heavily in the stock market and I still buy/hold/develop domains...
Firstly - nothing changes overnight.
Secondly - I have no statistical evidence for this but I can pretty confidently say that AU domain have been increasing in value at at least 30% year on year for the last few years as more businesses try and get their hands on them.
Thirdly in aggregate my domain/development projects worked out having a price earnings ratio of less than 1 (ie they made all of their upfront cost of domain and development back within 12 months). For the last 2 - 3 years Australian stocks have had a PE ratio of 12 - 15...
Business online expenditure/investment is continuing to increase because that's were more customers are going.
So domains as an investment (especially if you are willing to develop) are still head and shoulders better value than stocks.
That said, they definitely aren't as good value as they were a couple of years ago when I was doing a lot more of my buying (but that's only because the prices have gone up).
Next thing to consider is that going forward growth is unlikely to be as rapid as it has been in the past, but that's just due to the law of compounding large numbers, ie you can't keep growing at 30% for infinity, and as something gets larger inevitably you have to accept slower growth.
WITH ALL THAT SAID, I do get you point over a long term horizon, if I was going away to jail today and I had to decide my investment allocations for the next 25 years between domains and stocks. I'd probably put 80% stocks and 20% domains, given that 25 years is a LONG time in the technology arena, and domains may have indeed have become old technology by then, but if they hadn't they would be SUPER valuable given their scarcity.
If the timeframe switches back to 3 - 5 years then I'm quite confident premium domains will easily outperform stocks as an investment.
The danger to domain values, as I see it, is if apps rather than websites start to become the major destination for users
The real danger to domains is businesses not getting a return on investments from websites (ie users get all their needs fulfilled by sites like Google, Amazon, Facebooks, Ebays, etc). If users continue to browse websites and businesses get value out of those users they will continue to invest in the branding and marketing of those sites which will include domains...