I agree with @Rat3dE . I can't speak for everyone who runs [[The Tabernacle at Pendrell Vale]], but it's a reasonable choice in specific matchups. Like you said, the HollowVine decks don't run a ton of mana to support a Tabernacle, but you'd bring it in only against decks that are even less equipped to handle it.
It looks like partially The Tabernacle is a response to a specific metagame. Is this still the case now?
I don't play online and very irregularly play in paper so my knowledge of the metagame is quite outdated. Nevertheless, I was under impression that Dredge is getting leaner and meaner as a response to fast combos and mid-range controls, not to mentions thanks to new forces (let the force be with us).
I noticed that in the Vintage Challenge #12130342 Dredge and HollowVine 6-1'ed. It would be interesting to hear from the players, but I have no idea if PTarts2win or WingedHussar has a TMD account.