workerd is really far from production-ready Workers replacement, and seems to be very specifically scoped in such a way that essential parts of why Cloudflare dares to run it are not included in the bundle.
My best guess is you're talking about sandboxing, specifically how we defend ourselves against malicious tenants. Indeed, a lot of how we defend against that is not in workerd, and fundamentally can't be, because it's more than just some code, it's a process requiring active management.
However, you only need that if you have untrusted tenants.
If you are using workerd to self-host your own applications on non-Cloudflare infrastructure, then this isn't a concern for you. You don't have untrusted tenants.
If you are hosting untrusted tenants, then you can put workerd in a micro VM, the same as you'd do with any other popular runtime.
My best guess is that you are suggesting that we should open source our multi-tenant hosting technology, along with workerd.
But this doesn't make sense. No popular JavaScript runtime includes multi-tenant hosting technology. Multi-tenant hosting is the responsibility of the hosting provider. workerd is compatible with other providers' multi-tenant hosting approaches. You do not need our specific technology in order to run Workers apps on other hosting providers, and in fact would not even be particularly useful for that purpose.
workerd is really far from production-ready Workers replacement, and seems to be very specifically scoped in such a way that essential parts of why Cloudflare dares to run it are not included in the bundle.