Tcl has had threads that were subinterpreters since a decade ago or more. I find it quite ironic that Python, it would seem, is reinventing it, only in a less elegant way.
I'm personally glad that Python is (poorly) copying this feature from Tcl. This means it's closer to the time when JavaScript (poorly) copies it from Python ! ;-)
Actually Tcl has been successfully using the model of one or more interpreters per thread since Tcl 8.1, released in 1999, a full TWO decades now.
The functionality was always there it just rusted over from disuse.