Let me add a little more...
I'm attracted to LBC for lots of reasons but the one that stand out the most is that it supports nesting to arbitrary levels. That's important to me as it allows me to construct a launch structure that respects good UI design (limited choices per level, limited number of levels) and that reflects my application usage patterns. If FSL Launcher allows arbitrary nesting I'd probably not be exploring LBC.
When I have had some more time to think about it I'm going to suggest that you incorporate tabs (in the strong sense of the word - tabbed browsing, tabbed file managers, etc., not as you currently use the term) as an alternative to menus. I'm not ready to yet as I have not thought it through enough. A node type of "dock" would give me a partial means to explore how I would use tabs but without the work of implementing tabs.
Another reason to justify a dock node type: you clearly have a sense of the importance of regularity and generality in design - it is obvious from looking at LBC. Including a "dock" node type is just one more instance of that generality and will produce options for use that you and I probably cannot imagine at the outset but which will accrue as others explore it.