The problem is that by then, current programs will be out of date, and the new ones will be flashier and more resource intensive. The MacPro will still deliver a smoother, faster experience.
False: current programs won't be out of date by then. Current programs don't need Rosetta, and I doubt there will be a major processor upgrade within a handful of years which will negate the ability to run 2010-on programs.
Sure, newer programs will always be flashier, but they have come to a point where everything aside from professional video and CGI are hitting a ceiling with function. Web stuff will always evolve, true. Anything with basic writing and graphics and data shoveling is pretty much closing in on a natural limitation, so for 95% of the market, a MacPro is completely over-blown computing.
The MacPro will always deliver smoother, faster, but how fast do you need for the majority of work? So few people need that. Double the speed of the current MacPros and what do you have? A great video editor, a great CGI machine, perhaps. PS filters going from 5 seconds to 2.5 seconds isn't that big a deal-maker. Back in the days of wait-10-minutes-to-fill, MacPros were luxurious for anyone doing professional work in graphic, forget video or CGI. Now, and onward, they will become "mildly better" for the vast market majority.
Computer hardware on desktops is hitting a natural boundary at last. I've seen it progress toward this point. 10 years ago, a "MacPro" (Power Mac) seemed like heaven compared to the iMacs. That doesn't hold true anymore because of capabilities of programs being easily met by processors and memory. The industry is going to change away from the steady pace it progressively, routinely took over the last 25 years. We're right at that peak, at this moment, where the shape and function of computers will morph into something a little different.