It's very relevant to electronics stores like BestBuy as they want people to buy new things. But 1080p to 4K is going to take a LOT longer than SD to HD did. Even in that transition, some folks were happy with fake HD (720p) as opposed to full HD (1080p). The majority of laptops still ship with fake HD screens.
Far less than 1% of homes have a single 4K panel in their home. Far less than 1% of content is available in 4K. So, yes, "To the vast majority of consumers, 4K is currently irrelevant." The key word here is currently. A year from now -- not "2016", I mean 12 months from now -- there may well be enough 4K content to make it worthwhile for upper-middle and upper-class families. But there isn't right now. And a year from now there will be a new set of TV top devices.
You have to sit very close to even a 60" 4K TV to experience much of a difference - you essentially need a TV that dominates your living room to really discern the resolution leap. The performance penalty for games is severe enough that nobody's in a hurry to release a 4K console, so Apple gets a lot more advantage standardizing around one resolution.