In the interest of full disclosure, I will state that I haven't yet read all the recent postings, just a few, so I will need to go back in order to comment fully and intelligently, but I feel the need to add this which has been kicking around in my head for some time;
While I can see that there may have been something in the revelation that awaits the SHs at Raftel to make the Roger pirates hold off revealing the history (and Ray did indeed imply that was the case when he said they and the Ohara Scholars may have been too hasty), I also think there were strong hints that part of the reason they held off was related to Roger's illness, and that Roger may have run out of time.
There is also the possibility that more time needed to pass for whatever needs to happen, or even that Roger himself, while being a "D," wasn't the "right" D (perhaps because if his illness and lack of time?), and that may be why Roger needed to wait for that right man–(fate's golden child)--as WB stated he was during the war. Aside from the illness, it's possible that the wait was needed because the plan laid down on the Poneglyphs and in Raftel was a very long term plan, and needed many years to come to fruition. It's interesting that the Poneglyphs act as a sort of giant "Treasure hunt," if you'll forgive me, in the way of those party games, where each clue leads to location of the next clue. (ETA that of course I know that they don't lead one to the other, but I believe that it's been stated that a person needs to read them all to get the full history, unless I am recalling incorrectly--so please correct me if I am wrong--some treasure hunts work that way too, where each location has a clue to the treasure or answer to the puzzle or what not) In other words, there was delay built in to the very system represented by the Poneglyphs and how they were located. Whoever found and followed them was not meant to find them quickly or without peril. They needed to see the world--all of it, apparently, given the locations of the stones--and learn along the way. There appears to me to be a method to that madness. Why? Training for a future leader? Seasoning to make better, more informed decisions?
There are many pieces of evidence, and some seem contradictory. It will surely be a kick to see them all come together at the end, in a fnely woven masterpiece as only Oda seems able to weave.