A report by the WAG in 2003  discussed access to CIA, and the tone of the report indicates that they consider CIA to be a major destination (although they do not specifically state that). The tail end of the report mentions that the contractors' preferred option is a new trunk road toward the CIA (section 4.6.3), and that the route to the airport, both in the short and longer term proposals, be considered for adoption as a trunk road. (section 5). I don't know of further developments since this.

Also, the map's data is as of 2002, and may not be current.

It's been a while since I drove along the M4; does anyone recall if distance markers (or whatever the technical name for the signs) list distances to CIA as well as other locations? I know that CIA is signposted, but so is Cardiff Bay ("use junction 32 for the Bay"), which I'm sure we agree does not warrant being listed separately.