So Cas should be promoting their brand in that area and if successful, presumably they will be on a par with Warrington catchment
Clearly you don't know much about the area if you mean Ponte, South Elmsall, Knottingley etc as Cas are already targetting there, and have been for years, just as are Featherstone and Wakefield. There's no way any of the 3 could claim these places as an exclusive catchment area. As others have pointed out there's a lot of affinity for the area's other teams (and now even Leeds due to the house buiding that has taken place over the last 15 years or so) in these towns which would not only take years to change but also require the other 2 teams to disappear. Even if folk don't actually attend PO Rd or Belle Vue they'd be even less likely to go to Cas. Further afield in the Selby District they face competition from Leeds, Doncaster, York and the 2 Hull clubs for (potential) supporters.
As l'ange has said, the combined support for the 3 Wakefield District clubs is pretty abysmal for a so called hot bed of the game, although to be fair, it's the same story for most of the 'heartlands'. The sad reality is that in the UK RL isn't anywhere near as big, or important, as many on here seem to think it is.