No drawback if you have the hardware and know how to do it, but those are major obstacles for the vast majority of people who use Google Drive. Signing up for a hosted instance is much easier (and not even more expensive)
Nextcloud is already on the list but I just wanted to mention that self-hosting isn't the only way to use it. Frankly for the price of a hosted solution it isn't worth it unless you already have a server for other things.
The article is unclear but that's my reading of it too. It's obviously infeasible to sue everybody who does this (especially if you're a public figure, it would be hundreds of lawsuits) so I think the endgame is that if the content doesn't have a signature, we assume it's fake.
Goatse doesn't look the same as I remembered...