You won't be able to take the newer Rebellion content back into previous versions. We've had to update data formats and many other components for the new content which the prior releases wouldn't recognize.
One thing for sure is that with the new shader, particle effect and effect will know some huge change...
Do Stardock plan to release a new forgetool in the same time that rebellion ??? If the .fx files are modified, the particle forge will not work anymore... reference files will help modders too... maybe update the tutorial .pdf in the same time since they are not anymore accurate since sins 1.1 ( switch of the alpha cl with the red da was never included )...
Since Rebellion is the last expension for sins, it is certainly good news for modders... after release and a few patch, modders will be able to work on a final version of their mod... until sins II is released 