[ecky-l]

"well .. i am a big believer in the two layer separation"

I believe in this too. Not only two layers, if necessary there can be more.

For that to work, well designed interfaces are quite necessary.

"tcl + c .. are not exactly that and i believe a more modern combo will be better"

You don't necessarily need to reinvent Tcl in another "more modern" language to achieve that. You can compile Rust crates to dynamic libraries (.dll, .so) and use c types, or ffidl in Tcl (http://elf.org/ffidl/) to call the functions in your DLL-crates. Or write a small Tcl C extension to wrap function calls in the Rust code. That will do, without rewriting Tcl in Rust. For the other way around you can always call the Tcl library via its DLL interface in the same manner (which is the way to embed Tcl interpreters in other programs).