Just a quick post - I found an academic article on Druidry and ancestor worship that turned out to be a good read, so I thought I'd share for anyone else interested:
The Role of Nature, Deities, and Ancestors in Constructing Religious Identity in Contemporary Druidry
That's the pdf link, there's also a Quick View on Google. Celtic Reconstructionism gets a passing mention (in Druidic terms, as per usual), but otherwise it mostly concentrates on Druidry in particular.