I have been eagerly awaiting some official documentation surrounding VI plug-in development (both client and server), ever since Andrew Kutz's amazing job of reverse engineering the framework. I guess the document release probably got lost in the publicity surrounding the Virtual Disk Development Kit released a few days prior to the release of this.
Peronsally I think the whole VI plugin idea is nothing short of a stroke of genius. What better way to combat the potential for the likes of Microsoft to relegate VirtualCenter to the background by building full VMware infrastructure management into SCVMM, than to open up the VI management framework in such a way. And the architecture... as much as I might accuse VMware's tools of lacking enterprise scalability from time to time, they've absolutely nailed it this time. I mean, look at this (from the document)
Outstanding! On the coding side, it looks so straight forward that even a hacker like me should be able to put something together fairly easily... running off the example in the document, you could pretty easily add a context menu item to ESX hosts that fires up the out of band management web interface (ie the iLO page for HP kit) of that particular host.
Hopefully it won't be too long before the framework moves out of experimental status, and we start seeing 3rd party tools leverage the functionality. I've already seen the Xsigo plugin and it looks great.
Download it here