Bobby G, (and others) Partial answer to your questions about why the two kits cannot be combined.
It is two of these...One Tool Bank for each kit. Run separately.
Then, the older Duster tooling needs to be removed, and half of it discarded, and combined with the new tool Demon components. Not Impossible, and could be done, but costly and wasteful. Better really for you to do it yourself. Round2 Is getting those folks who want the superdetailed new chassis and new body, halfway there by you combining both kits.
For everybody else who just wants a Demon for the shelf, they have filled the bill.
These kits will sell out fast, I predict.