The main Olympic stadium does not have to be the athletics venue though - just the venue for the ceremonies. This is what happened at Rio where the Maracana was used for the ceremonies (70,000) whilst Stadium Nilton Santos (42,000) was the athletics venue.
Suncorp could be increased to 60,000 for the ceremonies. Look at the Gabba on Google Maps - it’s hemmed in by main roads on two sides. I could see it getting a decent tart up to say 40-45k, and being used as the Athletics venue.
The real chance here, is if we have Brisbane 2 by that point at either Ipswich or Redcliffe to push for it to be a soccer and Rugby 7s venue to try and get a good 25k second stadium somewhere in Brisbane.