Hoopie, it is an interesting question. Townsville has a bigger population than Cairns and the Fire have had FAR more success than the Taipans so why would the "move" not be in the other direction? The whole idea is reflective of deeper issues and attitudes that are at the heart of the "problem" with the WNBL. Those who think that such an idea is a magic bullet are ignoring several key factors, particularly when they think that the AFLW can just be copied across to the WNBL.
The first is evident in your question in that the AFL did not have any risk in alienating supporters of an existing club. For this idea to happen in the WNBL, 4 clubs would have to move or disappear, 50% of the clubs. Even if this was a "one step back, two steps forward" scenario, could the WNBL survive the one step back?
The second is the money. The AFL is so far in front of every other sport in the country it is not funny. Even the NRL has not yet replicated the men's comp in terms of teams. When you look at the metrics in terms of attendance, memberships, viewer numbers and budgets, the AFL outweighs the NBL by a factor of at least 5 and up to 10 times in some areas. That means they can both afford to subsidise the AFLW, but also a low percentage "conversion" of fans still results in a decent figure.
Thirdly, we already have people complaining about the level of talent but now 25% more talent needs to be found to add in another 2 teams, not to mention any further ones if the NBL itself expands. All this while in direct competition for talent with the juggernaut that is the AFL(W).
Fourthly, how does running double headers increase the money? You might save a little on game day costs but how do you increase income? Do you charge more? Quite a few NBL teams are getting close to sell outs anyway. As a one off they might work for novelty value but not the solution long term.
The solution long term is one which involves a lot of work and patience as societal attitudes to female sport (unfortunately) slowly change. As long as fans constantly compare female sport to male sport, female sport is going to struggle. The simple fact is that elite level males will run faster, jump higher, kick further and throw further than elite level females. Basketball is a classic example. You won't see any slam dunks at a WNBL match so if that is what drives your fondness of attending an NBL match then a WNBL match is not going to get you as excited. It is why I would wholeheartedly agree with those who asked questions about the Ninnis appointment. Yes the sport is the "same", but the tactics are different enough because of those athletic differences that just dropping a top level coach in with no previous experience in the WNBL is no guarantee of success.
Tennis is probably the "gold" standard in terms of a "big" world sport that has a high level of equity so I would be doing a deep dive into fan attitudes in that sport before looking at the AFL. Why do people not make a comparison all the time between Sinner and Sabalenka? How often do you hear or read comments that Sabalenka could not beat my U-14 son? The AFL is big enough to withstand those attitudes and overcome them with sheer financial might and will, but basketball needs a more nuanced approach.