That was exactly what I was thinking. Combination of longer fork and angleset at -1 or -1,5 degrees, you will get a slack front. I just don't know which frames to look for... And i might not get 3" tires but 27,5x2,8 should be ok in most 29er boost frames. (?)
Maybe 2016 trek remedy 29er with, 160mm fork and -1 angleset you will get towards 66-66,5 area...