Believe it or not I’ve read all of these arguments before, but unfortunately I don’t believe Sunrise to be consistent enough of an anime company to actually look into the writing. Since a lot of what I want to say would just reiterate what’s already been said I will instead point you to two very good pieces of writing on Lelouch being alive or dead.

First a personal favorite of mine is

http://omaemo.dasaku.net/2008/09/30/code-geass-r2-25-for-dummies-or-its-not-the-horse-cart-stupid-the-ending-explained/

which goes into quite a bit of detail on why Lelouch could supposedly be alive.

I personally believe that Sunrise’s original intention was to have a dead Lelouch. I know them too well after watching Gundam 00. They think that killing a character gives a series depth and in some ways you have to show death in a war story, however, they made a big mistake by thinking that’s all they needed. Sunrise can really do whatever they want at this point. I would be more surprised if they left him dead when they could milk the franchise for more money. Still, I’m a big believer in writing your own ending for R2. It seems like you want me to help convince you that he’s a live more so here’s another link.

http://animeotaku.animeblogger.net/2008/09/code-geass-r2-25-so-is-lelouch-dead-or-not/

though it might be broken now. Good Luck!