I'm looking forward for this feature for a long time. Although I've read all in this topic, I consider this feature very important for many reasons. Why not implement this for God's sake? It's stupid to encrypt all notes that I consider important. A passcode is a very good option. I'm a developer and I know that to develop this feature isn't a task of another world. If you are .NET desktop dev. you can code this in a few days. Unfortunately I have a professional duty until December 15th and I can't offer myself to research the specific library and code this as a volunteer. But if this is not done until there, I will volunteer and try do this by myself.
I hope some employee see this topic and send to its boss to consider this feature.