I think it's highly unlikely it won't have any issues and be 100% ready. After all it's not called "final". It'll probably need tens of bugfixes post-release. The rate of bug-squashing is significant, which means that mainnet functionality will surely uncover more bugs that weren't discovered in test-net scenarios. But unlike network forking issues with MN payments, these bugs do not carry the same weight. Forking is a game-stopper. Darksend bugs aren't. You patch them and move on.