A pain point in moving from flat land maps such as Leaflet is Cesium's apparent lack of support for using HTML in labels or billboards (as reflected in this forum and Greg Thompson's post here: http://blog.aviture.us.com/2016/12/01/cesium-labels.html). Since this is something I need for one of my projects, I've built a rough example of such a capability and am leaving it here for anyone else needing it.
https://github.com/ThadThompson/CesiumHtmlBillboards
Cheers,
-Thad