I've been looking into this sort of thing recently as well. I'm unsure if the raspberry pi has the requisite grunt for mount control, guiding and tethered image capture, so i've come across a few alternatives which although more expensive offer more hardware features and better performance:
Pandaboard
Beagleboard xm
It might even be possible to run OpenPHD and an indiserver on a 'rooted' android smartphone - that is another option i am looking into.
The challenge is (as you have already mentioned) that you have to use linux. Image capture and guiding is now incorporated into the latest version of Kstars, as is a GUI interface for indiserver (see here:
http://indilib.org/). Dithering, and PEC are probably the main features that i think are still lacking from the existing linux software offerings.
Failing all this i might just give in and get a miniITX PC and install win7...