Chromium's IndexedDB implementation is rewritten on top of SQLite, to replace the previous implementation that uses a hybrid of LevelDB and flat files. There is no change to the Web API. This is expected to improve reliability and, to a lesser extent, performance. For now this is applied only to in-memory contexts such as Incognito mode in Chromium and Google Chrome. This limits the impact of any new bugs, as well as puts off the need to worry about migration of existing data persisted to disk.
Chromium's IndexedDB implementation suffers from poor reliability and maintainability because it is highly dependent on a database engine (LevelDB) that is not maintained or supported, or as featureful as a full RDBMS. Many sophisticated web apps report high rates of missing or corrupt data, and bugs in the aging backend are hard to find and fix. SQLite is a more suitable replacement for long-term maintainability as it has an active development team and community, and its features like native support for transactions should yield improved reliability.
Samples: https://evanstade.github.io/web-storage-demos/idb-txn-scopes