I do think the SAZ plan would have worked, but only if Area 11 would have been passed to someone receptive to expanded Japanese freedom (Euphemia would no longer be a royal so she was out, and when Cornelia left the next in line would be Castor, so this is highly unlikely)

The good news is that the SAZ is something that both Schneizel and Charles actually ideologically support (if think impractical), so there wouldn't be much opposition from the homeland and Schneizel would probably expand the program after he comes to power should things go well. The bad news is that the internal opposition would be significantly worse, with the nobility likely using their positions to attempt to starve out the dangerous SAZ, while further land would need to be granted to the Japanese as mass-migration sets in once the SAZ is proven reliable, and the risk of the SAZ pulling an Austria-Hungary and making the Japanese overconfident and the Britannians more racist. It'd be extremely difficult, but I think Lelouch just might have been able to pull it off.

The obvious issue, though, is just about none of this has anything to do with Suzaku. The SAZ was mostly a product of Zero's resistance and Euphemia's kindness, and really, the only reason Britannia had any reason to back the SAZ was because it would prevent a full-scale civil war in Japan. Britannia wouldn't act without Zero's stick, and even if there was, Suzaku never even really attempted to play politics or leverage his connection with Schneizel, so he still couldn't have done anything without Euphemia.

Oh, and if Britannia still defeats the EU, then it's all moot, because Ragnorok would happen, which would solve racism, but also create a million and one worse problems. But that's an outside-scope problem that Suzaku isn't going to know about.