The COLLADA to glTF converter online tool allows you to convert your COLLADA models to glTF for use with Cesium. Simply drag-and-drop your COLLADA file (.dae) and any images it references by zipping them together. A self-contained glTF file will be downloaded once the conversion is finished, and a model preview will be shown below.
Cesium has introduced full support for glTF models. A demo with example aircraft, ground vehicle, and character models is available. There is also a tutorial on how to use the Cesium API for glTF, and a tool to convert COLLADA to glTF (based on COLLADA2GLTF).