Interesting idea and while I think it would work better with quest driven solo play, instead of exploration driven solo play - a "late" reveal at the end of 16th level would work for a exploration style 20th level campaign.
I have made campaigns using this type of strategy - have someone powerful i.e. a God(dess), Dragon, Greater Demon, NPC want to do something and then cascade a chain down of events down on how it would work and who would oppose it. That gives a set of allies and enemies. I found those type of campaign scenarios worked pretty good.
I'm going to start play testing the quest system once the party hits 2nd on the second level of the dungeon. I basically want up to two successful quests per level and I've split the quests into two series. I happy with the first series, but am ambivalent about the second series so I think I'm going to phototype it in actual play and see what it feels like.

