There are technical limitations there, the only really viable way to signal from great depths would be sonar. A radio beacon would be useless under 4000m+ of wa

There are technical limitations there, the only really viable way to signal from great depths would be sonar. A radio beacon would be useless under 4000m+ of water, and there's no realistic way to ensure that a small bit of wreckage ever surfaces to make a radio beacon work. There's also no legal requirement, there is no FAA for submersibles. Now something like an airplane's black box has an underwater locator that works for a while, but there's no particular reason to expect that a meaningful and timely search can be made at the sort of depths a submarine like the one in the article works at. tl;dr Rescue and recovery at 4000m+ is pretty much never going to happen, although it is technically possible, and there's no reason to worry about safety standards for something this niche, or limited to militaries.