To answer the first of your many questions:
Yes, a syntax virtually identical to yours, that allowed multiple namespace
declarations in a single attribute was considered. The resulting syntactic
problems swayed the WG away from that approach. (Some of the issues -- you
now need an internal quoting mechanism, or a careful proscription on the
legal characters in a URI, in order to allow proper separation of the pairs.
It gets even messier to come up with a syntax to declare the default
prefix.)
I couldn't understand most of the rest of your questions.