By the way this library name syntax is currently supported by try.scheme.org if you want to try it out. For example you can type at the REPL:
(import (github.com/gambit/hello demo))
and the interpreter will fetch the library directly from that github repository. Read the tutorial on try.scheme.org to know more about how to write and use hosted libraries.
I would rather see the URI enclosed in double quotes, which would
eliminate concerns about conflicts between Scheme identifier syntax
and URI syntax. It would only be slightly more verbose to say
(import ((uri "https://github.com/gambit/hello") demo)),
but would be even clearer.