I've been thinking how far extensions can be stretched to. To be honest, I haven't looked at how the extensions worked yet, I've mainly been working on a design.
So anyway, when will the limit of extensions be reached? I mean is it possible to continually write extensions without touching the source code at all, or at one stage will this have to be the case?
What if you wanted to create link directories, a gallery, and other larger applications for Vanilla. You think this could be done AS an extension without touching the core, or not?
Vanilla is pretty neato when it comes to extensions, but of course I couldn't think of everything that extension authors might want to do for this pre-version-one installation of Vanilla. I'm quite proud that there haven't been many of the problems I had anticipated with developers - but that being said, there are certainly limits to what you can do.
For example, all extensions rely on existing pages. If you wanted to add a new page, you'd have to literally create a new document in the root. There is no extension to add new pages - only the ability to add new controls (And alter existing ones).
another good example of a limitation is the one unipus is trying to do right now (http://lussumo.com/community/comments.php?DiscussionID=662) where he wants to alter the appendix contents. Sadly, the appendix contents are not editable right now (though they will be in the next rev).
Which brings me to my final point: As people develop more and more stuff for it, as long as they stay in touch with me and make requests for things, I'll seriously consider all of those requests and will continually massage the core to make it as extensible as possible.