Thanks for the suggestion! I need to look more at the codebase to actually see where this pattern would benefit this project. Because after an hour-ish of pondering I don't have a conclusion that's very useful.
In general, I tend to avoid Callables unless they're very simple (I use a Queue of Callables for the floating synergy text in my game). I've worked with too much clever code (including my own) that was too hard to debug or add to.
It sounds like your use case is solid. You can store Signals as variables and emit them (queue.pop_front().emit()) but it sounds like you probably want dynamic arguments so Callables sound like a great tool for your use case.