>1. changing the doc charset to 10646 doesn't have any implications on
    >currently deployed browsers, etc.; that is, it doesn't invalidate any
    >current practice (other than the current hodge-podge of usage re: numeric
    >char refs -- which is broken in any case).
    Well, as the mapping from document character set to system character
    set is not specified in SGML, and hence, is system dependent, I think
    most current practices, even numeric character references, are legal
    with a document character set of ISO 10646.
No, numeric character references *are* broken if they are used in
reference to the system character set rather than the document character
set.  The standard is quite clear on this.
Glenn