My initial thoughts after reading the blog post, just to poke holes in their new product:
1. Costs. This can save time on read, but it is also introducing additional writes to the database, that can be pretty expensive. PlanetScale can scale horizontally, but have to watch out how much it is going to be paying for the extra machines. (Albeit- machines are usually always cheaper than developers)
2. Consistency. It was not clear if it is going to make committing transactions slower to keep all the views up to date, or if the materialized view is running slightly behind real-time.
2a. And how does the materialized view handle large/slow transactions? Is there going to be any kind of serialization locks? Are the views correct inside of the transaction?
3. Predictability. Query planning is a necessary hell, and different queries might have different patterns that might introduce slightly different materialized views, that could have been maybe served under the same view. Increasing the cost.
3a. SQL Server took a slightly different route lately for performance, in which queries will have different plans depended on the table statistics. I wonder how such a feature would play with Boost, and if slightly different query plans might generate different materialized views.