The issue isn't criminals communicating over E2E encryption. The issue is that social media uniquely facilitates fandoms for crimes (mainly CSAM) where criminal influencers can easily build audiences for fame and fortune. This is only possible with the specific combo of E2E _plus_ VLOP.
If VLOPs can't use E2E encryption for their social graph interactions, (or, a warrant could open a backdoor) then these criminal influencers would no longer be able to grow an audience as easily. They can't simply make their own VLOP, just like the free speech absolutists failed again and again to create their own Twitter.
So, if the result of this legislation was that criminal networks all switched to Signal or a proprietary E2E comms app, the world would actually be a better place. They could still communicate, but they couldn't recruit as easily.
Sufficiently large? The software is there, I could deploy something like that in an afternoon. I'm not a criminal organization. Anyone can deploy their own e2ee infrastructure.
But where will you put the server? Not in the USA, that's for sure. Not in the UK. Not in Europe. Maybe you can broadcast your encrypted messages illegally on shortwave radio, until the FCC catches you broadcasting illegally on shortwave radio. Maybe you can bounce them off the moon (that's a real transmission technique) or hijack someone else's satellites (more trivial than it sounds because a lot of them are quite dumb). Or you can put a server in somewhere like Myanmar where they won't care about servers hosting E2EE apps, but they also won't care about strange men in black suits turning up and stealing servers hosting E2EE apps. Either way you'll have some difficulty.
You could just use onion services to to hide the server, and store some backup onion services (whose private keys are kept offline) within the application or its files. When the server goes down due to seizure, you spin up a new one under the backup service's pubkey, and sign a list of new backup keys which will also be kept offline until the next seizure.
You could also combine encryption with steganography, if you strip non-random 'protocol information' from your encrypted bits. Doing that, it would not be easy to prove that you are sending encrypted messages at all without having obtained your keys.
