One thing, which may be sort of a special case, that you should probably try to handle is merging 'document wide' style changes (such as changed color schemes or whatever) with content addition/removal. So like:

         version a
        /         \
       /           \
  add slide    change style
       \           /
        \         /
         version b

If there is a way that version b could have the new 'document wide' style change applied to the new slide automatically, that would be great. This is an issue that I very frequently run into when collaborating on slides, one person is working on adding unstyled content while the other is working on the look-and-feel of the slide deck.

Of course a style change could include things like font size changes that could break the layout of the new slide...