At the moment I don't see any problem because there's not a stable way to ask for jemalloc explicitly, but this does seem to be a reason to take pause at further stabilization. If we were in a place where all Rust users were expected to have access to the alloc_jemalloc crate in the sysroot, then Fedora not building it would be bad for us.
Personally, I'm in favor of moving in a direction where Rust uses the system allocator by default, there is some stable way to ask for a different allocator, and jemalloc is just a crate on crates.io.