@tmichellemoore @jasontucker My Tweets are almost always syndicated via POSSE from my site to Twitter, but for those prior to circa 2015, I do have an archive if someone comes up with a simple tool to do that sort of direct import. I’d probably want to pick and choose which ones were public however. I haven’t used that particular Twitter importer, but have used Sternberg’s Instagram tool as Instagram doesn’t have an official API for crossposting.
If you really want native ActivityPub mirroring of your site on Mastodon, you might try @pfefferle’s ActivityPub plugin (along with his NodeInfo and Webfinger plugins). I still need to tinker with my own set up for better formatting, but you could follow my WordPress site @chrisaldrich
A while back I did set up a system that uses IFTTT to target my micropub endpoint for syndicating some content from silos that don’t have good/easy APIs or methods into my website. Generally I do this as private posts so I have the data and selectively post it as necessary. These days I primarily do this with my Hypothes.is annotations to my site, though only a tiny fraction of the 12,000+ is publicly available: https://boffosocko.com/kind/annotation/. Currently only about 1/3 of my 45,000+ posts are publicly viewable on my site.
Eventually someone might build Micropub as a Service so you can sign up and give it social silo accounts to have the service PESOS copies of your content to your website.