You probably talking about service virtualization. I have some plans to dig into this space, but later. For now check this https://en.wikipedia.org/wiki/Service_virtualization and http://hoverfly.io/ in particular.

I don't think it has much to do with virtualization, if I'm understanding correctly. You can think of it as the inverse of what your replay tool does. If you think of a service that does transformations on data:

Req --> Service --> Rep

Your replay service is a synthetic Req. I think the parent is proposing synthetic Rep. This can be useful in many scenarios where you effectively want to mock a downstream service.

The industry buzzword for this is 'service virtualization' as mentioned above.