Currently Cesium is using raster images from OpenStreetMap, but they also have vector tiles. Is it possible to add this to Cesium Ion, so we don’t need it buy/host by ourself?
That sounds like a good idea! The only issue I can think of is that CesiumJS doesn’t directly support rendering those vector tiles right now. So I’d say it’s on the roadmap but not in the immediate future.
Here’s the Cesium vector tiles roadmap:
Which I’ve just bumped with this idea.