There are still some things to consider:
1. One of the system tables (built indexes) was compact. For now, we just added value column to it to make sure it's backwards-compatible, but we might want to make sure it's just a "normal" table and doesn't have redundant columns.
2. Compact Tables were building indexes in KEYS mode. Removing it is trivial, but this would mean that all built indexes will be defunct. We could log a warning for now and ask users to migrate off those for now and completely remove it from future releases. It's just a couple of classes though.