anyone know if it's possible to create a "configurable" typescript source Pulumi provider? looking at the provider server source, it seems like it is just not implemented https://github.com/pulumi/pulumi/blob/master/sdk/nodejs/provider/server.ts#L93 while the Go server source shows it implemented

Yeh it's not implemented, it's missing from the TS interface for providers. I think it would be pretty easy to add, would be very similar to the other non-config methods. Feel free to raise an issue or PR if you feel comfortable filling in those methods. We can probably find the little bit of time needed to get this in.