You can read up on the details in the post on Meta.SE if you're curious.
We'll maintain an evolving migration schedule to show which site is supposed to switch over to CommonMark when.
We've got to learn and reflect as we're starting out migrating the first few sites, that's why you'll see that the migration schedule is still pretty empty except for a few sites.
Physics (both, meta and the main site) are going to be among the first sites to be migrated and we've scheduled them to be migrated on Thursday, June 4th, 2020.
Why start with Physics?
We've tested the migration thoroughly on data that resembles production data of some of our communities. Still, we know that certain sites use different styles of writing and there's a chance we're going to detect some issues that we haven't found yet when running our tests.
Physics is a site that's suitable for fast feedback for two reasons: it's a site we can migrate quickly with its ~400k posts and it's a site that makes heavy use of MathJax.
Don't worry, MathJax is going to keep working after the migration. However, we want to be double-certain that we're not missing any edge cases, that's why we want to migrate a site with MathJax support first to spot edge cases early and get them out of the way.
Can this break existing posts?
We don't want to break hundreds and thousands of posts. That's why the migration will only apply updates to those posts that will look exactly the same after being updated to CommonMark. As part of the migration, we'll detect if a post changes visually after the CommonMark update. If it does, we won't update the post automatically and investigate what's going on.
What if stuff goes wrong?
If things should go horribly wrong, we've got an automated rollback in place that will undo the migration for all posts.