For G5 characters, clothing was made by creating an upper and lower part. This was very restrictive because the upper and lower not only defined the clothing but also the body shape. Thus a Chuck sweater would look really odd on Gwynn.
For CC characters (pre CC1.5), users can use predefined bases and apply some opacity to customize the shape. This is restrictive because users can not make fully custom clothing.
For CC chaarcters (post CC1.5), users will be able to create custom CC bases which will work with CC characters. This, however, is restrictive because such clothing will not work with G3, G5, G6 or DAZ (G1, G2 or G3) characters.
The solution is to implement clothing as props but still have them conform to any character. An excellent example of this is present in DAZ Studio where a user can take any mesh and fit it (using an automated utility) to the mesh of any character. If the character is morphed (body proportions changed) the fitted mesh adjusts accordingly. If the character moves, the mesh moves accordingly. Such "clothing" could then be used by any character (G3, G5, G6, CC, DAZ or other) instead of having it limited to one particular character type.