The Ancient One Listed at: $15.50 The Ancient One is an 8/8 for only 2 mana, but you need at least 8 cards in your graveyard for it to attack or block
So long as your deck is full of creatures with CMC 3 or less, Bygone Bishops requirement to Investigate isnt too troublesome
I do feel though they may be viable Standard and Extended options, but because of the extraordinary power-level of Extended right now, I think that perhaps there will be too many unfavorable match-ups, especially the modified Elfball, numerous artifact combo decks, and maybe Zoo, but if the deck can be modified to a state where it is a tenable Extended option, that's terrific in my opinion
Obviously this again depends on the use case of your cube but i would make the argument that for a 100% drafted cube having 3-5% powerful sideboard specific cards would improve the overall play and drafting experience vs 0%
This effect was so strong that it is likely we will never see a direct reprint of it on any future card without any massive downsides