I was thinking square bases would be perfect, atleast from a production stand point if we would switch from round to square. Octagon would be the next best choice, but would require GW or us to get them from another source.
Edit: 20x20mm bases for mines/escorts/fighters/bombers/transports, 25x25mm for cruisers and some defense platforms, 40x40mm for battleships and some defense platforms, 50x50mm for rare stuff like planet killer, hulk, others.