Well, first let me extend your explanation of the rationale for /usr/share: the reason for having a place to store not-executable shareable data is that in some network environments, it helps to have to maintain only one copy of this data, on some file server somewhere, which then gets mounted over the network to every machine. We need to keep /usr/share separate from /usr/bin, the rationale continues, because our network might be heterogenous in executable formats. In other words, some networks cannot maintain only one centrally-maintained copy of /usr/bin because some machines need, e.g., the x86 version of /usr/bin and some need the ARM version. In contrast, every machine can mount the same version of /usr/share.

Now suppose you are an admin for a network in which the numerical software foocode is a big deal. the software contains a large read-only database of numbers, which according to the logic of the FHS goes into /usr/share/foocode/. Now suppose that some machines upgrade to a new version of foocode which for performance reasons stores integers in some specialized format, not the ones-complement format that has become something of a standard. So now, if we continue to apply the logic that motivated the creation of /usr/share in the first place, we need a place to put numbers of the new format so that they are kept separate from the numbers in the old format. Thus /usr/share/ones_complement/foocode and /usr/share/new_format/foocode are created. Suppose further that yet another version of foocode is released, and again that some machines are upgraded to it and some are not. This new version introduces a new, more performant format for the database in which the numbers are stored. Well, if the old format is called the 'hyperbolic' format and the new format is called the 'elliptical' format, then the logic that led us to create /usr/share leads us to create /usr/share/ones_complement/hyperbolic/foocode, /usr/share/ones_complement/elliptical/foocode, /usr/share/new_format/hyperbolic/foocode and /usr/share/new_format/elliptical/foocode. My point is that at some point you need to move to some way of assigning 'attributes' (and "read-only, shareable, non-executable" would be an example of an attribute) to files in some way other than putting those attributes in the name of the file. It would have been better for that point to have arrived before the FHS caused programmers around the world to have to type /usr/share/emacs/23.3/lisp 500 million times when /emacs/23.3/lisp would have done.

What would this other way of assigning attributes to files be? A detailed explanation would be too many words for a HN comment. For the specific problems mentioned in this comment, namely, centrally-adminned file servers, you probably make your net-mount command more complicated like they did in Plan 9.

ADDED. div and mod are well know numeric functions, right? The mere fact that some group of people would like some convenient way to refer to all the numeric functions does not justify requiring every programmer to write numeric/div and numeric/mod (or numeric :: div and numeric :: mod) every time they want to use or refer to one of those functions. I say the same argument applies to /usr and /usr/share.