Well, Ubuntu was able to make their own startup/login menu with about as many features as the Gnome built-in version, but without the bloatedness. So it's doable with enough effort, that much is known.

Oh, while we're at it, with regard to Hurrian's mock-ups - I like the white icons the most. Which is why I'm saying this stuff should just be integrated into the theme structure (speaking of, MohammadAG, why did you hardcode the red background into the lockscreen [if you did; I'm trusting the guy who said you did, at least, until you say otherwise]? It's available by default in most themes [I don't think many theme makers change that one from the default, and if they did, what better background to use than that?].).

Also, for a lock screen, I personally think text is better than images. But if MohammadAG wants to go the image route, I say make text and icons in the mockups, and make both toggle-able.