It's the wrong abstraction layer for a heartbeat signal. That can easily be done by the application if it's needed. TLS and DTLS should provide encryption wrapp

It's the wrong abstraction layer for a heartbeat signal. That can easily be done by the application if it's needed. TLS and DTLS should provide encryption wrappers for TCP and UDP. That's it. Sure, it's convenient to have it already available for you to use as an application developer, but critical security software needs to be kept as small and simple as possible.