Safety critical systems should not rely on transport layers that are guaranteed to fail.

Go invent a transport layer that will never fail, and make yourself rich.

Because right now, there is no such thing.

Everything can fail even down to individual capacitors on the board but that doesn’t make the failure probabilities or failure mode equivalent to something like email that is best effort only and can be actively blocked by things like spam filters that aren’t even under your control

"Loud noises and flash bright red lights" is an industry- and regulations-accepted transport layer for a life-or-death signal.

Email is not.

Audible alarms, failsafe heartbeats and scheduled networking are not new technologies.