Got a couple for you:
Craftable/Somehow-obtainable Square Lights (Simple Lights as marked in store) once Facepunch gets their shit together and actually finishes them. (We talked about this one evening and that's what you said. I've seen them in use on @theattackchef's base thing, and helped him with the wiring this wipe, and they work VERY nicely. Ceiling lights in their current state are unusable for anything but massive buildings with multiple floors, and making these small lights available to everyone to use in place of them would be very nice.
Re-introduce the infinite fuel on Tuna Can Lamps from a couple years ago (but not for Spotlights) as a means of providing outside area lighting until the Square Lights are properly released into the wild. Again, outdoor (and in general) lighting at the moment is pretty much unworkable and this would be a decent quick-fix just until Facepunch gets themselves together and gives us the Square Lights. Seems like in place of any kind of lighting a LOT of people are switching to using dozens and dozens of christmas lights, and that just looks terrible. Plus, I haven't found a good method of lighting my helipad yet.
EDIT: Another one I've just thought of, but still unlikely for implementation:
Cap Shop for low-value/holiday/normally unobtainable items e.g. Square Lights, Door Closers, Fogger-5000s, Graveyard fences, small shelves, fishing rods, that sort of thing.
This last one I'm not really sure about, but I'll test the waters and throw it to the wind and see if anyone else likes it:
Enable the JPipes Christmas Lights on pipes config option so as to prevent bad things happening to people who fly close to the ground near a quarry with a lot of piping around it