It seems that nowadays you could in theory write web apps pretty much entirely in JavaScript. You mentioned Node.js for server-side logic. Then there are data s

It seems that nowadays you could in theory write web apps pretty much entirely in JavaScript. You mentioned Node.js for server-side logic. Then there are data stores that support JavaScript as a native query language (MongoDB, CouchDB...). For the client side, you can send an almost empty document to the browser and build the UI entirely in JS. Projects like CouchApps seem to head into that direction. However I'm not convinced that it's really a good thing for separation of concerns. You made a comparison with GUI development, but actually it's not uncommon to use a separate language to specify layouts when creating GUIs (Qt, Android...) The reason for that is that the declarative style of markup languages can often be a better fit than describing layouts programmatically. As for databases, it's great to have a (more or less) standard interface to query relational database that can easily be used from virtually any programming languages and from the command line. A lot of web apps are not limited to interact with a db and the filesystem but also need to interact with legacy systems. Less technical people might also want to be able to use off-the-shelf graphical tools to query the database. That might be a reason why ZODB, a Python-specific data store, hasn't been tremendously successful, despite meeting your requirements (notwithstanding scalability perhaps).