I depend on a mountain of C and C++ code to not only not crash, but to also not have any subtle memory errors which might allow a packet from the internet to run arbitrary code on my machines. Failures of that sort are disturbingly common.
You stand to gain more by people modernizing their existing code -- even, compiling their C code with a C++ compiler, and then improving that, as happened with excellent results in gcc and gdb -- than by hoping a vanishing few will switch over to a wholly new, unfamiliar language.
Liiterally millions of times more benefit.
In some possible futures, Rust code may take up just a bit of the load. The most value would come from its displacing C and Java in new projects.