Any news about how to make use of GL_OES_EGL_image_external?

Hi.
I want to render a texture that's constantly updated outside unity by a video player contained in an Android plugin. The update is done in an arbitrary thread (should this be UnityMain?). I know how to hook the texture (using Texture2D.CreateExternalTexture after getting the handle from the plugin).
I managed to create a shader that uses "#extension GL_OES_EGLimage_external : require" and I see no errors in logcat about compilation, but the texture shown is black. Also, if I use the built-in unlit texture shader, the texture shown is plain purple(the smaller cube).
In the bottom-right is a GLSurfaceView from Android side (I added it as a child of UnityPlayer's root view for debugging)

Shader:

 Shader "Fast" {
     Properties {
         _MainTex("Base (RGB)", 2D) = "white" {}
     }
    
     SubShader {
         Tags { "Queue" = "Geometry" }
        
         Pass 
         {
             GLSLPROGRAM       
 
             #ifdef VERTEX
             varying vec2 TextureCoordinate;
             void main()
             {
                 gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
                 TextureCoordinate = gl_MultiTexCoord0.xy;
             }
             #endif
            
             #ifdef FRAGMENT
             // require GL_OES_EGL_image_external so we can access the external texture data on android's GPU
             #extension GL_OES_EGL_image_external : require
             //precision mediump float; // added
             varying vec2 TextureCoordinate;
             //uniform sampler2D _MainTex;
             uniform samplerExternalOES _MainTex; // replaced above line with this in order to use GL_OES_EGL_image_external
            
             void main()
             {
                 gl_FragColor = texture2D(_MainTex, TextureCoordinate);
             }
             #endif
 
             ENDGLSL
         }
     }
     FallBack "Diffuse"
 }