I think scilean is solving a different problem than the projects built on top of flocq and vst.
Scilean seems to be starting to make it possible to do scientific computing in a type theory, while flocq and vst are big steps toward correctness proofs of the primitives that are actually running on critical systems.
On one worldview, scilean's impact is greatest if it focuses on being a bare interface to common primitives than come in thru the FFI. Then, high level scientific logic could be proven correct and thru a precondition/postcondition schema gain confidence in the parts that get FFI'd out.
On another worldview, scilean ought to literally provide new primitives, replace blas or eigen or lapack, with proofs in lean replacing decades of battle hardened unit tests.
The second worldview seems more difficult to support. I roughly consider myself of the first camp.