I had an idea for the story that allows the past universe to still be mostly canon, but won't overwhelm new fans. Just skip ahead in time a bit, like toa kopaka said above, until everybody is peacefully living on Spherus Magna together, then have a new threat (the Element Lords?) pop up that requires the Toa to defend everyone again. Simple enough for new fans to understand, and still have the original story intact if they want to delve deeper into it. The post-2010 serials may throw a wrench into this theory due to them being unresolved, though.