Problems in a prior `Payload` PR

[hunterhector]

Describe the bug There are some fundamental problems found in the Payload implementation.

1. Referring to this a. The design requirement is to make Payload system generatable, but we cannot refer the generated code back in our source code. Creating this import cycle ourselves will simply create problems. b. We discuss that if we don't have anything special methods for TextPayload, then we shouldn't add them into top.py. But if we need to have them there then we should.
2. Some conversations in the PR are not resolved, make sure to resolve all conversations before merging.
3. Let's not use todo, if we don't track them in issues they will sit there forever.