I don't know that A&C necessarily covers cosplay, costuming or robotics.... They all seem highly specialized (like 3D printing) and I'm not sure what "makerspacers" are... they seem to also be called "Hackerspaces"
I certainly think that the costuming/cosplay could be its own proposal, as it's highly specialized and requires a lot of specific knowledge of different eras and different techniques. Currently it is generally covered in the Acting and Dramatic Arts proposal but I'm not sure how welcome cosplayers would be there.
Robotics is its own thing and is already in Beta.
And, as you said, 3D Printing is already covered in its own proposal.
If "makerspacers" is what I'm getting the idea it is, sites like Arduino (in Beta) and Open Source (also in Beta) cover a lot of what they do... but realistically, they seem to be a type of person that is a very broad category of topics and the point is to have a space where equipment and servers are available for the group to share the cost rather than each owning their own.
The building or facility the hackerspace occupies provides physical infrastructure that members need to complete their projects. In addition to space, most hackerspaces provide electrical power, computer servers, and networking with Internet connectivity. Well-equipped hackerspaces may provide machine tools, sewing, crafting, art fabrication, audio equipment, video projectors, game consoles, electronic instrumentation (such as oscilloscopes and signal generators), electronic components and raw materials for hacking, and various other tools for electronics fabrication and creating things. Specialized large-format printers, 3D printers, laser cutters, industrial sewing machines or water jet cutters may be available for members to use. Some hackerspaces provide food storage and food preparation equipment, and may teach courses in basic or advanced cooking.