To expand now I have had some sleep...
I believe there are licensing issues and it's a lot deeper than just Nokia. People collaborated to the Maemo project with Nokia and I am pretty sure some of those licenses are to not redistribute.
As I say the CSSU team at the time would have made a flashable CSSU image back then if it was allowed. Hence why you install it like an extras package.
Really many of these things you want to address should be "fixed" in their own software separately not bundled in some meta package like fixing script. I would be best to contribute to the packages themselves, maybe make a lists of what need to be done and take each package in extras at a time.

The concept has been around before, it's logical to want to have some way to reflash and put everything you want back as it was. These are where those perfect setup wikis appeared from years ago. Issue is everyone uses there device differently there are some packages you want to avoid or conflict with what you need. Also it's old more and more is breaking overtime and fixes are often short term this is why more focus has been put on Leste.

Many had hoped for a true successor by now but alas it's looking more like a Concorde moment.