Ontario I could see a slight (although very small) possibility for. A la China Airlines, WN could use ONT as an LAX overfill airport that is convenient for a different type of market (think places that are closer to ONT than LAX, especially factoring in traffic).
Denver, although it definitely has the connection possibilities and demand for it, doesn’t seem very likely with the 737. Considering that this flight would be slightly longer than Norwegian’s EDI-SWF, and that this flight would have more bags (bags fly free!), worse conditions (Hawaii is hot and Denver is high), it doesn’t seem all that feasible for a flight from DEN-HNL. Take LAX-HNL, for example on Delta. Their 737-900ERs end up going out with payload restrictions based on the fuel load, despite the fact that they have fewer seats per square foot (meaning less weight from passengers) and less fuel required (LAX-HNL is much shorter than DEN-HNL). If Delta can’t make it fly full, I don’t think Southwest could.