My opinion on aliases and such:

1) Storage in isc4.gdb (as an option?) sounds very good, though if the
security on the alias table is the same as on the users table, it limits
creating and modifying of aliases to sysdba. Is this a bad thing, or a good
thing?

2) Why have $ to indicate an alias? When a connection is made to the
server, the server can look at the remainder of the connect string and
decide if it's an alias or a file or a redirect based on this order of
preference:
Alias - check configured alias storage location(s) to see if an alias
exists with this name
Redirect - Check to see if the connect string refers to another server
Local file - If none of the above, try to open a local file

This way I could have an alias named "/path/to/database.gdb" which maps to
"/other/path/to/otherdatabase.gdb" in case I move a database and don't have
a chance to update all the clients.

-Mark