Turn that around: lets say you know Swift because you're an iOS developer. What web dev languages or platforms can you use? The same argument was made about No

Turn that around: lets say you know Swift because you're an iOS developer. What web dev languages or platforms can you use? The same argument was made about Node.JS, that backend services already had great languages / platforms / ecosystems. It's not about existing experts in the area learning a new stack, it's about enabling experts in one domain to reach 'good enough' in another rapidly.