A 'slide' mode would be great. If I'm swapping out a 2hp module for a 3hp module, having to manually move every module down 1hp is really fiddly.
-- stogoshuffle

It can be if you're manually dragging the modules. But the other mode is quick and works like you'd want here. Hover the cursor over a module, then hit either "," or "." to move it left or right respectively. Even if you have a pile of little stuff in a row, this can be dealt with in seconds by using those shortcuts.