Is there anyway one could get a sense if the PCB trace antenna on a module is good enough to work with a typical WIFI router/receiver in such a situation? Or do I basically have to built it and test to see?
The short answer is: Yes, build it and try it out.
The longer answer is that a good PCB trace antenna implementation isn’t really inferior to your other antenna options. The only catch is that you need to carefully observe any implementation details and avoid detuning it with nearby components or enclosure walls. Most vendors will provide a reference design with some guidelines (PCB material, nearby ground plane requirements, keep-out areas around antenna). Always start with that.
The reality is that you can’t make an IoT device work in every possible user scenario. I prefer to set a reasonable benchmark against my phone. If I can stream YouTube on my phone over WiFi in a certain location, my low-bandwidth IoT device should also work there. Your phone has the advantage of a highly optimized, sensitive front-end, but your IoT device has the advantage of ultra-low bandwidth.
Users can generally understand that if their phone can’t get WiFi in a location, it’s unreasonable to expect any other device to work there. On the other hand, they’re not going to be happy if their phone works fine but your IoT device cannot.