OpenSSH can already do all of these things that you listed.
You can manually sign certs for users and hosts with ssh-keygen but there's no distribution or automation included with openssh. There's a half dozen SSH CA solutions around for this, but none as polished as what teleport has.
Teleport's session logging is unrivaled by anything you can do with openssh and is one of the key reasons I'm looking to adopt it.
The reverse tunnel mode could be accomplished with autossh to manage a reverse tunnel, but that's also not out of the box.
Maintaining a CA (and dealing with cert rotation) is some work.
Other things are indeed just a flag or config option (like jumphosts). But it takes work for a sysadmin/devops to educate all engineers in the company and make sure everyone uses the correct setup and doesn't end up dropping authorized_keys around random servers.
It's not that difficult technically as it is socially.