While I completely agree with the principle, there may be practical issues for the glibc maintainers. Suppose, for example, that the use of the feature in a given way is an optimal solution on Intel processors but not on AMD? In that case, releasing the code might also be seen by some as enabling a campaign by Intel against AMD. If the glibc project does not have the resources to check, perhaps the best option is to start with a conjunction of feature and vendor checks, with the latter being expanded to include all vendors that have endorsed the change.