I don't think they'll go with no costumes. Maybe that's how it was in a previous script, but they're retooling the movie in light of the DC slate and it's going to a summer blockbuster so they want it to be visually appealing. I think Ayer is going to embrace the characters' costumes and comic elements. The villains are very individual so putting them in uniforms won't achieve much other than looking like the X-Men which doesn't really fit. They're individuals recruited for specific skills and forced to work together. Having separate looks conveys that better. They're not really meant to be a team since each one of them is expendable and they all have different agendas. The movie will probably have a bunch of different wardrobes including their own looks and perhaps matching mission outifits, but it won't be a team uniform or anything. It will be very temporary and mission-specific.