It would be awesome if we could "hijack" requests and serve different assets to that request, even if that filename exists in the ASSET_MANIFEST. An immediate use-case for this would be to serve newer image formats to clients that support them, such as WebP or AVIF images, even when a JPEG is requested.

The mapRequestToAsset would be perfect for this use-case, if it allowed this function to entirely override the requestKey. The code in this file doesn't seem to support this though:

Pseudo-code example if this were possible:

// handle images rewrite to webp
if(url.pathname.match(imageRegex)){
	// request for an image. Check if we can serve webp instead
	if(event.request.headers.has('accept') && event.request.headers.get('accept').match(/image\/webp/)){
		options.mapRequestToAsset = (request) => {
			const parsedUrl = new URL(request.url);
			parsedUrl.pathname = parsedUrl.pathname.replace(imageRegex, '.webp');
			return new Request(parsedUrl.toString(), request);
		};
	}
}

Note: This actually used to work in much older versions of kv-asset-handler:

Let me know if I can provide any more info here!