Dylan was going to be Newton's system programming language, and while the language group lost the the C++ team (Apple had two competing teams for the Newton OS), it was still NewtonScript for everything userspace, and it was getting a JIT by the time the project was canceled.
Objective-C is dynamically typed beyond the common subset with C, and was used even to write NeXTSTEP drivers.
I don't know how much of a chance Julia has against CUDA/ROCm/C++, especially now that everyone on the GPU space has decided to give feature parity to Python on their hardware, via day one bindings to the compute libraries and JIT DSLs, so that makes Mojo even less of a chance than Julia has.
Julia has an established ecosystem, and presence on the scientific community with ties to MIT.
Python is the champion, and most folks writing CUDA/ROCm/C++ are already using it.
So who would be reaching out to Mojo, instead of Python JIT DSLs/bindings or Julia, when having Fortran, C, C++ allergy?