Erlang needs a production quality web server that is a fully compliant OTP application, and mnesia needs to have its dependency on dets abstracted away so that other storage engines can be used (relational database of choice, dynamodb, etc.). This would give a web developer a single platform that is extremely fault tolerant and scalable. This sort of thing may be possible (by using an embedded web server wrapped in your own OTP code and by experimental mnesia extensions), but it wouldn't be easy to get it set up and working.