While it's true that the farther out from his death we are, the more likely it would've been that Steve would have continued input into the design of a particular product, the fact is that lead times on design, particularly hardware, are set in stone by technology and production capabilities years before they hit the store.The "four year plan" was a story started by a UK tabloid paper, The Daily Mail, the day Jobs died.
The only "evidence" of such a plan was some analyst's guess, but of course lazy reporters immediately repeated the article as gospel.
Before Steve died, he knew what Apple was planning for the hardware design of the iPhone 6th gen, 7th, and probably 8th gen. And the same goes for every other annual upgrade.
Now, when it comes to things like software UI/iOS elements, I'm sure the process is one of constant input and feedback, so his voice will be missed much sooner, but there are, again, basic roadmaps in place. Apple doesn't wait until one product is released to decide how they're going to improve on it for next year. Design and development are multi-year processes. Being the CEO and de facto head of the company after he resigned, Jobs was at the front of these decision processes.