It would be literally insane to charge $650 for a SWA CC and yet not allow the primary CC holder a guest (speaking to this part "Southwest lounges with unlimited complimentary access for the primary cardmember with complimentary food and drinks, wifi, and power outlets")
That said in lounges if they are really interested in it I kinda think they should look at airports that don't have a big presence in lounges and are also SWA dominant heavy ones to really get an idea of the interest on that since it would be available to a subset of passengers before they just start having lounges all over. The lounge game is crowded and SWA doesn't have the more upscale experience yet.