9th Generation Intel, relative to Intel Macs, is still fairly recent. Similarly, Apple is starting to be more preferential towards Intel Macs with T2 chips (and Apple Silicon Macs) for certain features. It seems likely that there will be a release of macOS that eschews support for Macs that do not have either Apple Silicon or a T2 chip before they nix support for Intel Macs altogether. I don't know how aggressive Apple will be in this, but they do seem adamant that we'll have a few more Intel Mac compatible macOS releases yet to come. I'd say, a MacBook Pro (16-inch, 2019) will have until at least 2026 to get the latest macOS releases (and then another two years thereafter of security updates on that last version).
The PowerPC to Intel transition was a different transition under a different Apple during a different time. There are over-arching similarities, but the timing on this transition is already not at all what that transition was. Therefore, you cannot make a reasonable hypothesis based on that alone. I'd imagine that the next time that Apple changes the macOS minimum system requirements, they will either (a) limit Intel Macs that are older than Skylake, (b) limit Intel Macs that are older than 8th Generation Intel, or (c) limit Intel Macs that don't have a T2 chip. Either way, we won't see a dramatic "no more Intel Macs" Apple Silicon only version of macOS for a while yet.
You'll definitely get 5 more years of updates. Unsure if you're getting too much past that. But, you'll still get two more years of security updates thereafter, so at least there's that.