I would be 0% likely to keep any original firmware in there.

The point is that it's known hardware that works with Sailfish and for which Jolla is making Sailfish build.

In practice that would be :
- Either hoping that Jolla releases a "Jolli I" (i.e.: a Jolla-branded iteration of the same hardware where they deliver the OS directly instead of going through Inoi, kind of like Jolla C vs. Intex Aquafish)
- Or manually installing some community rebuild.