I myself haven't done any major blogging in a while (Last year I started one and just used Hugo as a static-site-generator so no ActivityPub integration, but also ended up not really posting much), but from what I've always heard about WordPress the major "selling" point would be its vast ecosystem of plugins and themes.
But that ecosystem is a double-edged sword, because there is tons of malware for WordPress that comes in the form of plugins (I know WP itself used to be exploited a lot in the past, not sure what its reputation on its own codebase is these days).
I've not ever seen WriteFreely before, but I doubt its ecosystem is anywhere the size of WP. Whether that's a roadblocker is of course only a decision you can make.
I'm sorry that I didn't have much more to offer as an answer, but hopefully it's something at least!
In that case, couldn't you just use something like btrfs snapshots + Timeshift to pull this off?