No chat app needs a desktop App, they need a WEB app. Generally I’m against them, but in this case it makes sense. It makes cross platform trivial, and you would never really need to use a messaging app offline anyway, browser APIs have come a LONG way. It’s also Google’s core competency. So yes, I believe they 100% have the tools if they wanted to try.
As for integration, my point is: why would Apple bother integrating with Google’s suggestions? Google has a track record of abandoning standards and ideas at the drop of a hat. Why on earth would Apple spend time, money, and engineering talent on something that’s likely to become abandonware in 2-4 years time? That’s also assuming it’s a GOOD standard, most of the previous attempts had fatal flaws that made the product dead on arrival. If Google had something compelling, and gave us a reason to believe it would be around for more than a few years, I’m sure adoption would go through the roof, and Apple would want to integrate— Because it would now benefit them, they would be getting something out of the deal; More features, an established user base, etc.