Well, it seems many have put up their wishlist for features they would like to see in MySQL so here is my list. These are in no particular order of importance, just as they came to mind :)

1. Online Backup - This is currently being developed and it will make a big difference to many people currently trying to administrate MySQL. We can only hope that it gets done soon and is well tested to avoid any major issues.

2. Standardised HA/Replication - Along similar lines to the consistent online backup is that of consistent high availability, load balancing and replication. No matter what the engine being used, this will allow a consistent method of implementing these features regardless.

3. Plugin Architecture - I guess this is the underlying feature that will make the two previous point possible. I know this feature is in development also, but having it available and ready to work with in production would be great. I can see many other features coming into MySQL once this API is finalised.

4. DW features implemented - Some of the data warehousing features are greatly lacking in MySQL. Some of the new features in 5.x will help including index merge, view/trigger/stored procedures etc, but there is still much work in this area. Features such as bitmap indexing, proper subquery optimisation, and windowing features. Currently only GROUP BY ... WITH ROLLUP is implemented, and more of these DW features such as CUBE would also be very useful. (updated)

5. Parallel Features - This is a performance request on top of all the others. Making things parallel in any area that can use it. This includes parallel queries, optimisation and I/O as all would benefit from parallelism.