I did think about that, but I do plan to use hotspots for multiple things and have two frontend submission forms, one requiring a single category and the other requiring multiple.
My site is for bicycle touring; I'm having one submission form for people to pin a location for where they currently are so other members can get in contact and join them. This will only have one category. The other submission form I'm planning is for pinning different things; good hotels, camp sites, places to visit etc... so that will have multiple categories. Both areas will have a hotspots map only showing the relevant categories.
Not a major feature request (very cosmetic), as not that hard for a user to select a single category, but if something that could be added at some point then that would be good.
cheers Pete