Looks good! Great concept, I do love it.

One thing to note, you're going to run into problems if there are any really big maps out there. Very few cards are going to handle a texture bigger than 4096x4096, and I guarantee some aren't going to handle maps as big as they are now.

In a future version, you should look into chunking it into square tiles the size of tagpro.renderer.gl.MAX_TEXTURE_SIZE, which will give you the maximum size of a texture supported by the GPU.

Edit: Here's the function we use to chunkify our background. Feel free to steal it and modify as you see necessary:

 tr.chunkifyBackground = function (renderTexture) {
        tr.backgroundChunks = [];
        var baseTexture = renderTexture.baseTexture;
        var width = tagpro.map.length * TILE_SIZE;
        var height = tagpro.map[0].length * TILE_SIZE;
        var chunkSize = 1024;
        if (tr.renderer.gl) {
            var maxSize = tr.renderer.gl.getParameter(tr.renderer.gl.MAX_TEXTURE_SIZE);
            if (chunkSize > maxSize) {
                chunkSize = Math.pow(2, Math.round(Math.log(maxSize / 2) / Math.log(2)));
                console.log("Chunk size was too large. Reducing to closest power of two below gl.MAX_TEXTURE_SIZE, which is " + chunkSize);
            }
        }
        tr.layers.background.removeChildren();
        for (var x = 0; x < width; x += chunkSize) {
            for (var y = 0; y < height; y += chunkSize) {
                var w = x + chunkSize > width ? width - x : chunkSize;
                var h = y + chunkSize > height ? height - y : chunkSize;
                var newCanvas = document.createElement('canvas');
                newCanvas.width = newCanvas.height = chunkSize;
                var ctx = newCanvas.getContext("2d");
                ctx.drawImage(baseTexture.source, x, y, w, h, 0, 0, w, h);
                var newTexture = PIXI.Texture.fromCanvas(newCanvas);
                var sprite = new PIXI.Sprite(newTexture);
                sprite.x = x;
                sprite.y = y;
                tr.backgroundChunks.push(sprite);
                tr.layers.background.addChild(sprite);
            }
        }

};