No not really. Toowoomba Airport is under-equipped. Government repatriation flights might work to that airport on a very limited basis but international airlines are still going to fly to the major airports(outbound passengers out of Australia, freight carried alongside passengers in the plane belly). I don't think you can 100% rely on repatriation flights to bring Aussies home. You need quarantine within the metro area. I would agree putting them in a skyscraper with narrow hallways and recirculated air conditioning in the heart of the CBD isn't the best idea.

Even if the authorities ignored that, you still need to bring cargo only flights into the country as well, and the air crew need to be isolated. But Toowoomba would not have the logistics infrastructure, warehousing etc to support cargo to an adequate extent. Now you can perhaps argue that maybe Australia should manufacture iPhones etc to bypass that but that's impractical and a whole different argument.