The jump from SD to HD was huge. Everyone welcomed that. Not only did HD provide more resolution... large flat-panel HD displays finally made it economical to get a huge screen in your living room.
HD took forever to start catching on though (first hit the US in '98, 25% adoption in 2008, and we are currently at like 70-80% adaption depending on who's numbers you see), and if companies didn't just stop making SD gear the transition would've even been more drawn out. Without the federally mandated move from analog to digital broadcasting (which meant everyone needed to buy new broadcasting and receiving gear anyway so why not go HD) HD wouldn't have happened until streaming, IMO, because it would have been too cost prohibitive.
With streaming though, it's just more bits flying across the Internet. I mean, in something like 5 years YouTube videos when from 240p to 1080p and it all happened in the background. Same for when Netflix went from SD to HD and now to 4k. Little to no disruption on the consumer side of things (unlike the analog to digital switch).
Depending on how far you sit from the TV... you might not even see the difference between HD and 4K
I doubt people will actually notice (just like most people didn't realize they were watching SD on their HD TV) but they'll believe the marketing so they'll think they'll notice and that perception, plus our consumer-centric culture, is all that it will take to move product.
And then there's production. Shooting in 4K... editing in 4K... and delivering in 4K are waaay more intensive than HD.
The barrier for entry is actually surprisingly low. There are a number of 4k cameras out today including inexpensive GoPro's and DSLRs. 3D requires specialized products where as shooting and editing in 4k is just like HD (or even SD) just with bigger file sizes (and sometimes smaller file sizes thanks to better compression). I've got a 2009 Mac Pro and I can edit 4k on it in Premiere Pro so you don't even need a beast of a machine for it. Yeah, I have to edit at 1/2 or sometimes 1/4 res if I'm pulling enough streams, but even at 1/4 res that's still HD quality on playback.
Take a look at Craigslist ads in NY or LA and you'll see at lot of no-budget movies, music videos, TV pilots, etc., shot in 4k and looking to be finished in 4k. Need it or not, it is already on it's way to becoming the new norm.