It's crazy that this is only happening as of 2022, right? They could have kept a whole generation of web sites on WordPress by eliminating the MySQL dependency, and gained a performance and deployability advantage in the process. Even multitenant WordPress would have come out great with SQLite. I'm waiting for someone closer to WordPress to tell me how wrong I am about this, because I have to be missing something.
I'm not sure that it'll bring a lot of sites back to or keep them on WP, but it'll be great for testing. Much of it is always integration testing with WP because of how filters and actions work your code is rarely ever isolated, SQLite will make that much easier and faster.
It's also really not a big switch for the most part. I'm not aware of that many MySQL-specific things happening in WP. Things like fulltext indexes aren't in core, so it's really just using a different driver to get the basics working. I'm sure it would break a lot of plugins, but that's fine, they have platform requirements anyhow, adding "does work with sqlite" isn't a huge step and can likely be automated to a high degree (if the plugin never uses wpdb->query, ->get_results etc, it's compatible).
