Thanks for the Kudos, Fiskbit, and thanks for everyone for weighing in!
I'm going to leave this poll open for another few days, but I'd like to clarify a few things based on some excellent points that other posters brought up:
1. Even if I change the hotkeys on the galaxy map to correspond to control groups, the priority buttons will still be there. You'd just have to click the buttons manually instead of selecting them directly.
2. If we change to the control groups instead of the priority buttons, Alt + the 0-9 could work for priority, as Blam Stokel suggests (I had been thinking Alt was already used in combo with 0-9, but that is not the case).
3. I think I am going to add a "selected units" button on the galaxy map, on the left sidebar, which would work just like the current selected units button on the main view. I'm going to do this either way we go, because I think it will be helpful in general.
4. If the control groups hotkeys start working on the galaxy map, that does NOT mean that other quick-selection hotkeys will also work here. Quickly selecting other specific non-control-group units is not going to be something that is possible, nor is quickly dividing your ships in half or selecting just the first non-idle unit from your selection (another requested feature). Maybe we could make an exception for the selection-modifier keys, but those would be it -- we need the rest of the hotkeys for other functions on the galaxy map (primarily display button toggles), and I'm really not trying to duplicate too much unit management functionality on the galaxy map simply because you're doing those selections and giving those orders fairly blind.
My personal feeling is still that this will be more awkward than it is helpful, but I suppose that it's one of those things that only advanced players will really use anyway, so I could see the value of potentially adding it. We'll just see what the majority wants after a few days (or whatever -- I won't close this until I'm ready to work on it, or it's been too long to be relevant anymore).
Thanks for weighing in, everyone!