Mainly for educational reasons... educating myself that is lol. Just really intrigued as to how one goes about creating something like this and for some reason I've always found it easier to learn when working with things I'm passionate about Oh and also so I can explore the world I love in such a nicer looking environment! (even if it isn't really from a gameplay POV... yet!)
Anyway, it's awesome to see you releasing some previews (and more) of your work
That is an easy question to answer..to modify/adapt it in any way one wants for whatever project they see fit in the same way the Ryzom Core/NeL framework is open source and provides the full client build pipeline to all.
Not to mention having people be able to contribute to and continue the effort in the event that you get sick of working on it (not an uncommon occurance in the world of coding), and lets people open work on client support you might not be interested in (like a native Linux or a Mac port, or making it run well under WINE, or making mobile clients, etc.)
Thats a lot for one person to undertake, if they even wanted to, yet Ryzom Core is an example of how having this all open source has provided native support for Linux and Mac clients for the commercial version of the game, and the quality and capabilities of the content development tools for the NeL framework have advanced greatly due to being open sourced as well.