In reply to Ethical boundaries of typeface revivals:
The two designs you speak of are well out of any legal consideration, other than trademark. There's nothing to stop you making and releasing new digital versions of either Centaur or Goudy Lanston, and I don't see any ethical issue either. Even if there were strong copyright protection for typeface design, these would now be in the public domain.
You'll get snide comments about your lack of creativity or being an antiquarian hobbyist, but font manufacture, which is what you are talking about, is a craft, and there is no obligation to creative originality, only to doing a good job. An historic revival might not sell well, as Nick notes, but as you note there is still no good digital version of Centaur for text. If you find it pleasing and useful, that strikes me as reason enough to make one, so long as you are not kidding yourself that you will get rich from it.