there is nothing stopping your node-red executing docker commands and spinning up containers.
Another way could be to have multiple node-reds running and offload work to them using simple MQTT comms as a control + command API.
keeping everything in Node-RED will give the visual benefits.
company hat on for a moment - most of what you are asking (like spinning up more nodes, docker/Kubernetes orchestration) has pretty much been solved by FlowFuse (which is open source) - maybe worth checking it out?
