That's never going to work for the average person, sadly. And it misses a lot of social features that a lot of people (myself included) want from social media. Simply put, the UX is way too far off what people want and need.
It will, ISPs just need to start providing the basic hosting infrastructure on their routers again, like they used to. Thankfully we're also at a time where IPv6 is mature enough so that this is greatly simplified !
Wordpress doesn't have ActivityPub built in, it's a plugin in beta currently. Without AP, there is no client that can pull in website feeds and provide discoverability between WordPress sites, Mastodon posts, etc.
Back in the old days, activitypub was my Rss feed reader. Discoverability was driven by good old fashioned cross linking, comment discussions, and skimmable feeds from aggregators like the one we're on.
People love to reinvent the wheel and claim it's a whole new thing. No ideas on the web have really been innovative since the bubble popped. The innovation has all been on delivery and execution (not wanting to discount any of that).
Sure it is? WordPress updates itself and all plugins automatically. I've had Wordpress sites running for over a decade with zero security concerns ever popping up.