Here again, the merits of cross-classification dawn on me slowly.
Still, I can't help but think that the present versions of the fourth and fifth categories is unduly kludgy.  You say "Continental philosophy or in Arabic philosophy will presumably appreciate having one place to go, organized by the principles inherent to these traditions rather than by others' principles,"  but now you organize 17th/18th by time, then place, then name.  Presumably, the organization of Arabic philosophy won't be much more sophisticated.


Let me suggest that the organizing principle of the fourth category be: time then place.  And the organizing principle of the fifth category be: place then time.  Everything in the fourth category could then find its place in the fifth (automatically, perhaps).  The fifth category could contain, in addition, current approaches to such and such (Jewish philosophy, Continental).  There's no reason for the fourth category to be restricted to the history of just the west.  There will be lots of gaps, and where there is no philosopher, you don't need a category.  Still, this system will make things more intuitive for the categorizer and for the user.


A few caveats: I use 'place' a little loosely.  Sometimes it would be better to replace that with religious categories.  Averroes and Maimonides were both born in Spain, but its better to count them as Arabic (or Islamic) and Jewish than as Iberian.  Likewise with early Analytic and Continental (which aren't religious categories, but aren't exactly geographical categories, either).


And, in the twentieth century, there are more names, and the categories should sometimes go two deep before getting to names.   This is sort of a null case, and the fifth category classifications of Continental philosophy (for example) can be carried over cleanly to the corresponding branch of the fourth category.  (Aside from the impersonal 'Current Approaches to Continental'.)