look, the way I see it, they want to do a new title and 64 bit (kinda stupid that win 7 even has the option to be 32 bit unless its a phone or one of those giant phones. even then, i would imagine some idiot forcing it on to one of those lap-phones) and all that... Thing is, they've told us that the engine will require a big redesign to make it happen... assuming that's true, it'll be difficult to re-build sins to be 64 bit, design it to work on a broad range of hardware, add new content, balance everything, keep it on what I have to assume to be a smaller budget compared to other games, and get it out in a timely manner.
I think the idea with rebellion is to over-shoot the development a bit so that they have excess material for when they do build Sins 2 and can cut out some of the development time on that. The optimizations they make for Rebellion also are familiarizing the programmers with the expected tools and conventions so that the engine for Sins 2 can be a good fit and a smooth transition. Also, having people look inside it real good can also determine just how much needs to be redone to make it 64 bit and maybe determine what other features could be added as long as something near there is being redesigned...
So, yeah... I'm of the optimistic opinion that this is laying the groundwork for Sins 2...
then again, they are launching another rts game and i think that's supposed to use the same engine as sins... so...