I suspect the AFL would want to follow the money & the population & the power when it chooses a 20th team -therefore South Sydney Canberra Cannons (or Kookaburras - abbreviated to Burras, similar to Pt Melb. VFA). GWS becomes WS only, departs ACT. ABS estimates population of Sydney will be c. 7,000,000 by 2040 -with most growth in the west/SW.ACT so the Giants concentrate on Western Sydney?
7 games in SW/Sth Sydney, 4 in Canberra, 1 in Wollongong -or more? There will probably always be some Melb. AFL Clubs happy to sell 1 or 2 Home games for some moolah.
Sydney is the HQ of all media & most advertising companies in Aust. Over 60% of advertising in Aust. $ is spent by Sydney-based companies.
About 50% of the top 200 ASX listed companies are based in Sydney. Sydney is Aust.'s wealthiest city by far, based on real estate/lots of high paid jobs = an affluent, concentrated demographic "loved" by advertisers. Canberra has the highest mean wage earners.
GR AF is generally weak in SW/Sth. Sydney, but is growing. It is interesting & surprising that, for 2018, far SW Camden (where GR AF is strong, but Div.1 2017 Snr. Club not the best) was chosen for the new entry to the Sydney Premier Division. In 2018 in Premier Div., however, Camden has generally been competitive - many new good players came to the club (& money!?).
I don't think the ACT could financially support a Club on its own -not enough big. private companies there.
GWS & GC would have to be financially reasonably self sufficient before new Clubs are added -unless the AFL slashes its funding to the 18 clubs, by significantly capping & cutting the $180,000,000+ pa AFL Clubs spend/waste on their VERY bloated Football Depts. (No cuts to players' wages though).
I would prefer that AFL Clubs have only two players on the bench, subs only (to help eradicate the ugly congestion)- the traditional bench for over 100 years was nil, one, or two only. The AFL needs to revert to the traditional game of 18 v. 18, not 22 v. 22. This would release 36 extra players -and make it easier to find new, skilled players for 2 new teams.