Does it hurt to do this now? Will such stuff work fine on shipping
distros?
What would be the downside of doing this?
RHL9 already had NPTL as does RHEL3; any other 2.6 based distro has NTPL
as well. In addition you generally can't run "latest glibc" compiled
apps on older distros, compatibility is mostly unidirectional anyway.
And all newer distros have NPTL.