Again, great work. The 1.0.1 update seems to have fixed the few warnings and errors and now seems to work which is great. Don't let other people who give unhelpful or frankly rude feedback put you off - this is genuinely a brilliant plugin, so thank you for it.
I'm glad to hear that you'll think about custom post type support. I had a look around your code and a look at the codex and it seems that what you'll need is the get_post_types() function.
If you stick with your current programming methodology, this means you might have to dynamically generate classes for your custom walkers depending on what and how many custom post types there are. Probably not the most ideal solution, but it'll probably work. If I can think of a neater solution, I'll post back here.
Again, thanks so much for this plugin.