That means using existing designs with a die shrink or something is often the right choice when you’re shooting for the low cost portion of the market. The technology referenced here, enhanced memory tagging extensions, is a hardware implementation of tagging that requires a specific revision of the arm design and it’s a relatively new change (mte, the precursor to emte, is flawed and not used).
I'm writing this on a Pixel 8 running GrapheneOS, which I'm pretty sure is a "recommended" device that supports all the security features and is also multiple generations old.
If new lower-end devices use die-shrink versions of previously flagship SoCs, as you say, then I simply do not buy the notion that there's any good reason not to put a die-shrink version of this SoC in a new lower-end phone.