Yes, we have proven that shared-kernel multitenant is unsafe. The best example (though there are many) is the `waitid` LPE; nobody's container lockdown configuration was blocking `waitid`, which is what you'd have had to do to prevent container code from compromising the kernel. The list of Linux LPEs is long, and syzkaller crashes longer stil.
If they are using multitenant Docker / containerd containers with no additional sandboxing, then yes, then it's only a matter of time and attacker interest before a cross-tenant compromise occurs.
There isn't realistic sandboxing you can do with shared-kernel multitenant general-workload runtimes. You can do shared-kernel with a language runtime, like V8 isolates. You can do it with WASM. But you can't do native binary Unix execution and count on sandboxing to fix the security issues, because there's a track record of local LPEs in benign system calls.
