Sure you can. The services just need to agree protocols. The tech & cryptography part is not difficult these days. We've had guaranteed E2E for email since PGP in 1991, though not many people cared enough to use it.
None of the services you listed do it, but that's because they don't want to, not because it can't be done. It's a business decision problem, not a technical problem.
It's also a technical problem, the overall security model of these apps isn't just the E2E encryption, but e.g. Signal not saving attachments to local storage, message expiry (which inherently requires clients to cooperate).
None of the services you listed do it, but that's because they don't want to, not because it can't be done. It's a business decision problem, not a technical problem.