Would shimano ever give that up? No. All these companies pride themselves for being what the elites run. Dura ace would become a joke if no elites used it. The dura ace groupo upgrade is thousands of dollars (2k to be exact, it's the most expensive 100g you can pay for), & dura ace is high profi. So mo, too much brand risk. I mean, why haven't they stopped selling rim brakes already? It makes zero sense for shimano to do that.
Further, there are plenty of bike tire manufacturers making a variety of rim sizes. Some bikes can only do 25s max, makes no sense to only have a 28mm rim.
What's more, there's millions, probably hundreds of millions of older bikes that all need new rims every few years. For what you're saying to be accurate, no company would seize that demand and instead some sort of duopoly would instead opt for forced obsolescence. I don't see that as being the case (it is for thing like iPhones/cell phones, but the bike industry is very different)
