I'm afraid you're incorrect on that one. There is an obvious candidate with an identity and a natural fan base: Redcliffe. And it looks like Redcliffe are going to be announced as the 17th club this week, according to the SMH.
There's probably 2 things i'd say about that - Redcliffe is Brisbane urban fringe, although I believe it's a strong state league team. But do they have the support? Queensland rugby league attendances are difficult to find, but last time Redcliffe was in a grand final was 2018, and the crowd (against another Brisbane team) was 7500. I found a recent home final they played a few weeks ago and the crowd looks to be family and friends. So it's hard to see where 20,000 people a week are coming from.
The second thing is that i'm guessing whoever is behind the bid see that problem as well because they've rebranded in an attempt to capture the wider Moreton Bay region and (somewhat optimistically) the Sunshine Coast region. But they do seem to be well resourced, with the backing of a huge pokie palace. That's really the only saving grace, as they're going to have the same problem any state league team will have in any code attempting to jump up. They basically need to find a bunch of fans from nowhere. The only one that's really done it successfully was Port Adelaide, and as a comparison the 2 grand finals they played in immediately before their admission drew 46,000 each.