Okay, I did a bit of digging, and I think this should be quite doable. I have a lot on my plate, though, so while I'll try to keep tabs on this, don't count on me actually implementing it.
Here's how we could do it:
- Use the dbus-scripts package (currently in -devel; standard caveats apply)
- Listen on the "Coming" signal, as per the wiki page.
- That will give us the caller number. From there, we need to cross reference it with the address book, which should be doable as well, I would think. How one would do that, I don't know off the top of my head.
- Use espeak/flite/festival/etc to speak the caller name as listed by the address book

That should work, and it shouldn't be too tricky, I think. To the OP, and others, though, keep in mind that dbus-scripts isn't stable yet, so even if someone scripts this up tomorrow, I can't advise using it yet.

I hope this helps

Thanks to Matan, in this post, for pointing me in the right direction.