The most often cited Xbee example is the propeller project.
If you are considering Pi, you might also consider looking at the Yun, which is basically an Uno with a Linux side built-in. The Pi and the Yun would both need to talk to ST over the network, rather than Zigbee.
I played around trying to get a yun to talk to ST, but I was unable to find a decent example of a similar project to work from and then I decided to use a thing shield and had started to get it to work when you posted this and made what I was working on my unnecessary!
I have two thing shields and am using them for sensors in different parts of my house. I’d love to get a couple more, but they are out of stock. I find myself wanting to recommend arduino solutions to people here, but without the shields it isn’t feasible.
Xbee support would ensure that your excellent library continues to get out to great use!
Todd