I will implement this API starting next week or the week after.
I'll be working on the sub-tasks in this order:
1) the ones we require for the official Mobile app
2) the ones for which a patch has been submitted. I'll go through all of the patches. If there is no major changes required, I or the contributor will make the minor changes and we'll submit them for integration.
3) the most voted ones
4) the other ones ... but hopefully we will be stuck in 2) or 3).
Previously, I had time to successfully submit to integration 1 to 2 web services functions per week. I can see at least half of this list (51 subtasks) implemented for 2.3, the 1st of June.
Edit (24/04/12): this obviously will not happen for 2.3