On the subject of folk metal - Can you do some other border reiver songs - especially Tam Lin would be awesome.
A version of Blackleg Miner like that on the first Steeleye album would sound awesome too - copying that detuned banjo line would work so well with metal.
I'd love to do "Tam Lin"! Been wanting to do it for years, really. The last band I was in actually played "Blackleg Miner" a few times (and "Ye Jacobites by Name", as the drummer and myself were closet folk fans ;)), though you're right that adapting that banjo line could work well ....
I've haven't tackled any other trad pieces yet simply because I haven't been sure about the arrangements. I don't really feel like I did any
work to arrange "Twa Corbies" -- I just woke up one morning and there it was, asking to be played like that. :) I would definitely need to think about how to approach "Tam Lin", since even Fairport's pared-down version is pretty lengthy, and I think I'd want to vary the vibe a bit during the song ... though maybe the sensible thing to do would be to treat it in an epic metal way, like Dio-era Sabbath's "Heaven & Hell" or "Sign of the Southern Cross" vibe meets some of the proggier, more Tull-like bits of Iron Maiden from their last album .... Hmmmmmm! :)
I've long thought about a slow 4/4 version of "Scarborough Fair", sort of in the vein of Fairport's "Sailor's Life". And, though this isn't trad., the last band I was in also played a heavy rock cover of "Did You Like the Battle, Sir?" by John Richards and Bev Pegg, following Paul Downes's cover version. That works pretty well in a metalified context, and I'd love to revisit it .....