http://judy.sourceforge.net is a very fast, very scalable dynamic array facility. I wonder how it compares to Tcl's hashing and whether it is worth looking into as the basis for a more powerful array command.
http://www.snookles.com/scott/publications/pli2003-slf.pdf talks about how much faster it is in Erlang as compared with Erlang's builtin hashing.
-- Todd Coram