I don't really see a point in releasing a second SKU if it's just for graphics scaling.
I don't really see a point in releasing a new model of smartphone every year or less, and yet...
Another fundamental misunderstanding about this conversation is the idea that iterative consoles are only to get/"force" people to upgrade in shorter time frames. Let's set aside that no one ever forces you at gunpoint to be all "#shutupandtakemymoney" just because the nerd equivalent of Malibu Stacy getting a new hat happened. But actually, the opposite is a key factor in this, as well, that people want to upgrade LESS and iterative consoles give those people more options to loop themselves back into consoles.
The amount of consoles that Sony and Microsoft sold near the tail end of the longest generation in history without really even being THAT much better in price from the middle of the generation seems to indicate that, for a number of customers, they don't want/need to update their consoles every 5-6 years and were willing to stretch out the time they take updating to something new. PS3/360 were enough of a technological jump that, even when they were long in the tooth, it was still a good investment. But as we know very well by now, the times of bleeding edge hardware on consoles is over.
Let's say hypothetically I bought a 360 in 2008. I got a good 4 years out of it before new consoles hit the scene, but I want to get more out of it before I upgrade. Right now, the business model doesn't accommodate that very well.
And while it theoretically could accommodate that while retaining the current 5-6 year cycle, cross-gen development becomes a more difficult proposition when you're discussing a difference in hardware capability that's THAT wide. It needs that in-between step to make it viable, much like mid-tier PC hardware keeps the investment in multiple spec targets viable in the PC gaming market.
So it's 2016, I'm finally in the market for a new hardware box. Xbox One and PS4 are already horribly outmoded technologically. So my choices are either buy the aging hardware that will be outmoded in 2-3 years now, wait 2-3 years with nothing new to play or subject myself to PC gaming, something that I have avoided for years.
Again, the current business model gives 2 less than ideal options and an option that console makers don't want you to consider as an option because they run the risk of losing a return customer to the console market, a risk they can't take. Giving something new in that timeframe keeps people invested in console purchases when their purchasing choices don't align with the mandated industry schedule of every 5-6 years.
Lastly, the reason people buy consoles isn't because they want something that lasts. The malaise that happens at the end of a generation and the eagerness to trade up tells a different story of that.
No, what they look for is
a clearly defined upgrade path. PC hardware changes with a new GPU series once a year at the latest, so it's never clear when the real "game-changer" happens; the enthusiast press for PC gaming doesn't exactly help matters on this. Consoles make that clear to consumers right now. And that's something that cutting the iteration cycle to every 3 years won't take away.