Support for MySQL transactions in v5?
Database operations that insert/update rows in multiple tables should be grouped into a single transaction. This improves data replication and avoids data inconsistency from accumulating over time. This mainly affects content creation/modification.
Support for spatial data types and queries in v5?
I'd like to see full support for spatial indexes and queries on at least lat/long points.
Support for date and time types in v5?
I'd like to see full support for YEAR, DATE, TIME, DATETIME, and TIMESTAMP including fractional seconds for times stored in the database, e.g., TIMESTAMP(6) and TIME(6).
Also support many of the remaining data types as you can including binary and json data types.
I feel like the database layer has been neglected over the years in favor of the UX and hope that v5 will address this side of the SDK.