In order to load Elevation data with WCS, you will need to parse Geotiff client side. (Geotiff is a outpput format of WCS).
I’ve started a project called GeoTiffParser.js : https://github.com/xlhomme/GeotiffParser.js
My first attempt was to download a DEM from a WCS server (Geoserver) and obtaint elevation client side.
GeoTiffParser doesn’t handled all GeoTiff format (compression Tiling) yet ,… there is still works to do. But I succeed to load my DEM via WCS and obtain the elevation data.