I have thought about these issues a lot; especially lately. With regards to being able to scrape your data or just get your data back from 3rd party's, I think that's a losing battle. You need to be in control of your data before it gets to them. Web sites and APIs are constantly changing and sometimes just disappear. This idea of polling for changes seems very brittle and would never be up to date.

What I picture is an a program that you use to store your own microblogs, blogs, contacts, comments, etc. and then you publish to whoever from that app via their API or crawling.

Imagine you just created a new microblog entry. You can now either post to your Twitter, Mastodon, etc. accounts with the click of a button. You would have to poll for replies though and it would be up to you to store them if you wished (you probably want to if you are storing your replies). As an added benefit you could see the replies in one place instead of bouncing between two sites.

The point is, when you create the data, it's yours first. Then if you want to, you can post it other places. Tools like this are abundant for businesses, but we don't seem to build tools for actual people anymore.