In years, after it becomes 2.4
The next Lazarus version is planned to be released with FPC 2.2.2
If you need something a fix from 2.3.1, take a look if it isn't already on 2.2.1. If it isn't ask the fpc team to considering adding it there.
If you need a new feature from 2.3.1, then work with the subversion.