Yes, it is just a phase. However, unlike some fads, there are some practical aspects of it that will stick around for much longer. For example, what is practicle about air shocks, street blowers, or 33x15x15 tires? Nothing that gave them much staying power for more than a few people.
From the fad point of view, Foose is a designer. Like designers of the past, Exner, Buttera, Greenwood, it will come to pass eventually. Some will cling to it, most will pass on to the next thing. After all, there are still pro street cars out there, but they just aren't as plentiful. Yes, i think the 20" wheels will go away, the garrish paint jobs will go away.These are aspects of it that will not last.
From the staying power side of things, I think some will remain. More people are interested in decent, if not ultimate, handling that bigger wheel rates, tuned sway bars, and shocks will stick around. Even with a 15" tire, these improvements are subdued and not readily apparent until your drive. I've seen more inquiries about these items in the last two years than I have in the last two decades. Things like EFI and overdrive will continue to grow as the "drive em" crowd and events continues to be a major force in the hobby and these improvements become more stealth looking and less apparent. In time, I don't think it is unreasonable to think that we will see an under manifold efi system that will look original to all but the most well tuned in viewers.
Ultimately, the original, like stock build is always the home base of any trend that comes along. There will always be an attraction to and a large segment of the hobby devoted to stock appearing, stock built, as original vehicles. As always, the "pedigreed" cars will always command top dollars and be the pinnacle of the hobby with most the rest of us emulating them to some degree or another. Stock will never go away. It is the foundation, the base element that we have to have to create trends.