I would happily buy a "gold edition" featuring all three of the games, ESPECIALLY if it included tools needed to make more content for all three games. That would be ridiculously cool.
Unfortunately, it won't quite
work like that.
The Dev Tools will only work directly with Book III and its content. (BW has said he might later release an add-on package of Book II content (presumably just the maps, IMO), but I wouldn't even count on that.
Still, once the Dev Tools become available, I suspect a group of us will volunteer to "re-create" all the Book I areas (and possibly the Book II areas, depending on how BW handles that...) - it seems to be a high priority for a number of us to have the content for the entire
Eschalon gameworld available somewhat soon after the Dev Tools are released.
But, even if that happens, it will only be playable in Book III, is my understanding from BW...