[MichaelGG]

With ASP.NET, this is easy enough for JS and CSS bundling since that can be done as part of the runtime handler. (You keep the files on disk all normal, then specify which ones belong to which bundle names. ASP.NET does the rest for you.) So a simple if/else should be enough (I'm actually doing this for debugging on a site, just not based off of HTTP/2.)

Caching could be an issue, but if you're frontending with a reverse proxy, you could append another querystring parameter for http2 then do caching in the proxy level.