Both the hardware (base board schematics) as well as the software are open source. Let's say Kunbus goes down the drain and you hit an issue. Best case someone in the community has already fixed it. Worst case you'll have to hire a decent consultant. Show me another PLC that affords the same kind of vendor independence.

As to availability, the hardware is manufactured and assembled in Denkendorf, Germany, so the supply chain is short. The Foundation guarantees availability of the Compute Module 1 and 3 until at least January 2023.