About a year ago I was tempted to down scale due to space and lack of it. I abandoned 28mm in all periods except for my Russian Civil War collection which seems to be called Back Of Beyond these days.
Rather than down size why not look at changing rules. I do still have 6x4 table which I have to put up and take down when I game, but by going to rules like Mud and Blood and making games at a lower tactical level I can still use my 28mm figues. I can fit a couple of companies in a single file box which is plenty for a game and dosn't take up to much space.
When I was looking at going smaller scale I looked at 15, 20mm which there is plenty of. As for 10mm I think you would have to look at WW1 ranges which should cover all you needs for the bulk of your armies.