The two choices offered are a false delimma. The MILS kernels that came before seL4, like INTEGRITY RTOS and LynxSecure, had middleware to make deplpyments easier. The open-source solutions mixed standalone apps with user-mode VM's for Linux compatibility. OKL4 let one use drivers across them.
Looking at what's out there, I think GenodeOS should be mentioned for application-specific systems. They can even build some of their stuff on seL4 if you want.
I'll also add there's been unikernel projects that aren't in exotic languages. Even C++ (IncludeOS?). There's probably one in Rust by now. If not, it could probably build on Redox's components.
Looking at what's out there, I think GenodeOS should be mentioned for application-specific systems. They can even build some of their stuff on seL4 if you want.
https://genode.org/
I'll also add there's been unikernel projects that aren't in exotic languages. Even C++ (IncludeOS?). There's probably one in Rust by now. If not, it could probably build on Redox's components.