Namespace names identical to interwiki links should work, with the
namespace taking precedence. It may be surprising, but this is a
well-tested feature: we have a 'wikipedia:' interwiki link defined on
all wikis, and a 'Wikipedia' namespace on many of them, and everything
works fine. (Although you lose the ability to use that interwiki, but
it's also available as 'w:'.)
In this case you have an interlanguage interwiki link, which may
complicate things somewhat, but it *should* also work. (You do lose the
ability to have old-style interlanguage links, since you can't just use
another alias, but hopefully this is a minor issue.)
If you document specific issues, I think folks would be willing to fix them.
--
Bartosz Dziewoński