&gt; can modern complex, large-scale web apps be built with the tools we have today, be they Python, Ruby or Javascript?<p>For me, after the experience working on a startup that used TCL using an approach similar to AOLserver back in the first .com wave, web apps are always built with JVM, .NET or any other JIT&#x2F;AOT enabled language toolchain with JavaScript kept for its indisputable place on the browser.