slrpnk.net has some first hand experience for this, as @[email protected] already deployed anubis in front of lemmy-ui.
it wouldn't be that complicated to add it to lemmy-ansible if people are interested in having the option.
i don't see the argument for having this before user interaction though; the main goal of this is to fight malicious crawlers. for authenticated users, solutions like this are completely unnecessary as these can simply and much more efficiently be addressed through rate limits without putting users on low end hardware at a disadvantage and contributing to global warming.
I didn't mean only showing Anubis to unauthenticated users; this was in response to OP mentioning to add this before posting or commenting, which would be the opposite of removing it for authenticated users.