Ideally, InDesign would treat master pages like layers. In this manner, a variable number of master pages could be applied to any page, allowing for more efficient and quicker customization of page layout. For example, a user might set up the following master pages:

A-Body (1 Col.)
B-Body (2 Col.)
C-Body (Fig. or Table)
D-Header (Full)
E-Header (Partial)
F-Footer (Full)
G-Footer (Partial)

In this example, the many possible combinations, such as AD, AF, ADF, AE, AG, AEG, BD, etc. (based on layout needs) wouldn't need to be created. More importantly, as in styles based on parent styles, changes would effectively "cascade" due to changes in one master page, rather than requiring changes in every master page that contained any given element.