It will. The specification process needs to be informed by implementation and experimentation. When implementing a feature we'll learn all sorts of things and hit bumps that will help guide the design. Once we have a working implementation, it helps to be able to use it to answer things like:

- How does this perform on existing pages - How does this feel from a user perspective - How can I write pages that user this

Specification-up-front is very theoretical in the absence of an implementation. IMHO, where it's (rarely) happened in practice, the specification is often unimplemented. The value of a specification is that it allows other browser vendors to add an interoperable implementation.

Again, I'd like to stress, this is in the very early-stage experimental phase. We aren't dropping a feature that'll break the existing web.

Edit: To clarify, "implementation" does not necessarily mean shipped to users.