The thing to remember with the Dockers, is that its all based on BS.
"Oh, Freo's so special, Freo has its own identity & culture, Freo has such a proud tradition in Football" and its all a load of wank.
If Freo restricted their membership, to people with an actual connection to Fremantle (past or present) They'd have (pro rata) about 2,000 members.
Simple fact is that there is a HUGE amount of money for AFL in Perth, and a lot of local talent. They could have called the new team Innaloo or Cockburn, and it still would have worked Financially.
For a 2nd NBL team, you'd have to go much wider, and aim say for a "South of the River" team. (Yes, that's a thing, Perth is basically divided North & South)
Therefore pushing the idea that the Wildcats are the NOR team.
It would still be a tough sell, because the Wildcats' support is ubiquitous.
We have a much smaller population than Melbourne, yet have bigger membership than MU. That's not intended as a boast, just an indication of the market penetration the Cats have.
Also, unlike Melbourne, and Even Sydney, we've only ever had one NBL team. So there's none of the "My team were the Magic, I hate the Tigers/MU" type thing.
If you had the money, and could put the effort into Community development, it could be made to work, but would take a LONG time.
On the idea of a Dockers AFL - NBL tie up, yes it gives you access to money, expertise, and existing membership, but I don't know if that would be enough.