We had processor level branch predictors. Now do we not only pre fill the next prompt, why not just start generating the response as well?

Interesting thought at least.

I haven't noticed this yet. Was this added recently?

I think this analysis is spot on.

This isn't really convincing, since you can do this even without showing the prediction at all. Simply ask the model to predict what the user will send, then show the actual next prompt, and done. The only reason to show this would be to influence the user's next prompt, which the article doesn't touch on.