And why would Highlight.js be better than Google Code Prettify, considering that you admit yourself that you just heard of Highlight.js and therefore are probably unaware of its advantages/limitations/etc.?
You mention something about it looking "promising", but what does that mean? Moreover, why do we need something that only looks promising when we have something that already works just fine?
You also contend that it is "up-to-date". I'm not really sure what that means when it comes to a syntax highlighter. Are the syntax of various programming languages changing so rapidly and drastically that you really need to keep the code coloring engines up to date? Moreover, is Google Code Prettify out of date? And if it is, then why couldn't you (or someone else) simply submit a patch to the project, thus bringing it up to date and contributing something to the community at the same time?
You say that "its functionality is similar to that of Google Code Prettify", but that's not a justification for switching to something else. The functionality of Ubuntu is similar to that of Windows, but that in itself is not a good reason for switching.
To steal an explanation from Eric Lippert, features start with a "score" of -100. You have to provide good reasons why they should be implemented because implementing them takes time away from the programmers responsible, time that they could spend doing something else (like fixing bugs or implementing other features). And this is even worse than a regular feature request, because you're suggesting that we switch from something that works to something else that also works. That doesn't really sound like it's worth it to me.