Arima : in fact, WebGL shouldn't be faster with Ejecta, it should just be the same speed as canvas2d.
So, in the end, the canvas2d code is translated to OpenGL, and the WebGL code is also translated to OpenGL. The fact is that vikerman started to work on the WebGL portion of code way after the work was started on canvas2d, so the difference of semantics between canvas2d and WebGL explain the difference of translation (meaning their speed of execution) when they run with Ejecta.
That also means that using WebGL in your Construct2 code won't be faster than using just canvas2d (it's different than running in the browser). The only thing that won't work is WebGL shaders.