Swarm has a very special role, because it's custom-built to integrate in the Docker platform. Because it's so specific, it has a smaller standalone community than Kubernetes, but it makes up for it in focus and speed. You should expect a lot of bleeding edge features to ship in Swarm first, and a generalized version to land in kubernetes later. That's already been the case in the past: Windows support, secrets, node identity & promotion - those all shipped in Swarm first, then made their way to Kubernetes. Not because Swarm developers are smarter, but because they can focus on a narrower, more integrated problem set.
Longer term, I think all orchestrators will converge to look more and more the same. Orchestration will become a commodity, and it will matter less and less which orchestrator you use, especially to developers. But this process will take a long time, and in the meantime enterprises (our primary customers) need to deal with the situation on the ground, which is a lot of Swarm and Kubernetes living side by side because of historical decisions made in 2015-17.