Can you give me an example of what you would expect it to do that can't be done in the Playground and how you would use it?

It strikes me as quite an expensive[0] change to make just to support slightly different development models.

[0] Potentially requiring different code generation mode embedding type information and other run-time information that wouldn't generally be used and then having a system that can use the information to execute arbitrary code. It might be that much of this is already need for other purposes but I wouldn't assume so without information.