One thing to note here is that (unless I'm remembering wrong) LPC is designed so that when an object is updated, it always gets a new chunk of code attached to it, but retains its old data structures.
IE: If I modify a daemon (such as /secure/daemons/chat.c), and recompile it, the running object will now be using the new code, but still keep its existing data structures (IE: list of people who said something).
So, if you're going to start using raw function pointers in objects, you need to ensure that those pointers are always updated to point to the newest version of the object's code. Otherwise, you will end up with some objects using the new version, but still having call_out()'s or call_other()'s pointing at older code revisions.
I don't know how FluffOS implements this behavior, so it may be a non-issue... but it's the first thing that came to mind with your suggestion as a potential gotcha.