Here's a question... was there ever "the one" from any other era? Growing up, I thought the 1521 Electrolux models were "the one" from the late '80s and early '90s because I saw them in so many friends' houses, but I'd wager that the only people who agree with me would be other Electrolux fans. Some people probably even think the 1521 was the antithesis of "the one" from that era because it was based on 60s tech and ushered out the last days of the company being widely popular.
Dyson and Shark vacs are the only ones that get much commercial space today in magazines and especially on TV, so maybe they're "the one" that people will remember from ads, but I really don't know. My parents had both recently. The Dyson didn't fit where the old skinny Electrolux wands went (lucky me for inheriting the DJ), so they replaced it with a Shark that died after 3 years. Recently they went back to Aerus and got a battery-powered Lite Cordless.
A lot of the most popular new stuff (Shark, Dyson, etc.) has, like you guys have mentioned, some degree of planned obsolescence, so the most popular models will be few in number down the road. But then the well-built stuff (Miele, Aerus, etc.) has minimal advertising recognition, sells in small numbers, and lasts so long it rarely gets replaced. There's just not going to be much left in 20-30 years. The popular stuff will have mostly died, and everything else sells in small quantities. It's not like the old days when the Rainbow vacs, Kirby vacs, and the model G Electrolux vacs were both most popular and long-lasting. Now it's kind of one or the other. Either way, there won't be many copies left of anything over time.