I don't think my reply particularly addresses the idea of transposing stuff from open tuning, but your post reminds of how much open tuning has really thrilled me over the years. However, I think there are not too many guitarists including myself out there who have moved over to open tuning and play all their stuff in all keys in one open tuning. So the open tuning tends to quickly sound much the same from song to song and even with a capo, the properties are much the same. Nevertheless, I have to say that open G or D or Dadgad are great tunings and have a warmth to them that is more difficult to get out of standard.
I think Pierre Bensusan lives in one open tuning and can play in any key in open tuning, but I don't know anyone else who does. Sonny Landreth plays almost exclusively in open tuning but he uses a lot of different tunings - and he is an awesome
slide player.
I like Kirk's approach because he not only teaches us to play in regular tuning, he shows that slide in regular tuning when played right can sound awfully like an open tuned guitar. I believe that muting the strings is not only good for a clean sound, it actually improves tone 150% -- gives it a richness one cannot get if not muting. I have no idea about the musical physics of what happens when we mute out the other strings, but maybe if the pickups are only dealing with essentially one or two strings at a time, then we get that nice fat slide sound? I think also that being able to isolate single strings really helps us focus on vibrato -- at first Kirk's muting style in standard slowed me down a lot, and I am still a long way from being to play slide in any way fast, but the slowing down process has allowed me to really appreciate the quality of the sound and to really explore the range of tonal possibilities a little more.
Anyway I am off on a ramble here....
Thanks
Bearz