I want WOTC to make...another "Illithiad" series

[Fallen Seraph]

Then WotC still isn't giving you what you want, because while they aren't giving much fluff to speak of, what they do present tends to pin things down, precluding alternatives. A distinct monolithic origin story for 4e tieflings for instance, versus the wild and open variety that existed previously. Restrictive change while at the same time gimping on the flavor text. :/

The problem though with old fluff is that it had more integration with the mechanics, since it was more indepth, etc. So while yes there is a specific fluff for the Tieflings it is so brief and small that is much easier to eliminate and only look at the mechanics.