We need better keys, but demanding to be able to delete things from the Internet is a pretty hot take. There's no way to require relays / clients / the NSA / ransomware to behave a certain way. What's been said cannot be unsaid. People can choose to publish first to relays that (appear to) honor deletion. Most devs that push back probably do so out of concern for people fooling themselves into thinking that something has been erased. 

It's of course possible to build something more sophisticated on top of the current protocol. Something with limited distribution that's more likely to bitrot than survive. Not many relays are going to retain encrypted messages that are megabytes each, though archive.org might and the NSA of course will.

So, the energy is right, but taken at face value the demand to be able to delete messages doesn't make sense.