The points in your list can be easily implemented with the help of a plugin system. I know how most of the users out there feel to have an open source client to add customizations to it. That's why I will focus to allow a lot of modifcations. However, as you might already read out from my first post, I don't hesitate to share the information that I have extracted from the original client. And these information are probably what most people are interested in anyway. So why am I still going for closed source?
Simple: If reduced down, there are two factions of people. Those which focus to implement the ideas you're talking about and those that will use this ideas and indeed make money from the work of others (most likely how it is with eAthena/rAthena). I don't see the point why the second faction shall gain all the money without doing anything. I am working with a lot of interfaces that allow splitting very easy. Basically something like this:
As you can see, those people with ideas can hook everywhere they want to extend whatever they want. They can even completely reimplement the closed parts and use it for whatever they want. Let's say if I have implemented a class that allows a sprite to run around, but someone wants a 3D character instead, he can write his own implementation and exchange it without changing any other parts. Some could even change the rendering engine from Ogre3D to Irrlich, if they want to. They just have to make sure to implement the given interfaces, which will be open source since they are only guide lines. You might still wonder what to do when some interfaces themself have to be modified. Well, I'll add the ability to hook the core which might be risky. But I assume that the one who wants to change one of the interfaces knows what he does, so that should not be a problem.
This ensures that those with gread ideas have the possibility to chose if their implementations shall be closed or open source (for the same reasons as I have) and those that want only money still have to do something on their own. And even if I drop this project, as long as the base is done and available, anyone else can still further improve it. Besides that, you don't really have to worry. If I lose intereset or stop working on any of my projects, I'm gonna release the source anyway. So when I shall disappear, I will make sure to release the source (as I will do with WeeDiffGen). The only problem that might come up is the fact, that only a small amount of people are willing to continue such a project as soon as it gets open sourced.
I hope you can understand this decision of mine.