Related to a recent discussion on the php.internals mailing list, Chris Jones has posted about moving away from the MySQL extension in favor of the MySQLi functionality and the effort bubbling up to make the old functionality deprecated.

An important discussion on the PHP "internals" development mailing list is taking place. It's one that you should take some note of. It concerns the next step in transitioning PHP applications away from the very old mysql extension and towards adopting the much better mysqli extension or PDO_MYSQL driver for PDO. This would allow the mysql extension to, at some as-yet undetermined time in the future, be removed.

He links to a RFC that's been posted to help promote and push this idea forward with mentions of the "carrot" and "stick" methods for pushing users towards mysqli.

As always, there is a lot of guesswork going on as to what MySQL APIs are in current use by PHP applications, how those applications are deployed, and what their upgrade cycle is. [...] I want to repeat that no time frame for the eventual removal of the mysql extension is set. I expect it to be some years away.