It sounds like Frida and Cycript have similar goals - REPL and other cool applications are planned and meant to be built on top of the core that is currently exposed to Python, .NET and a browser plugin (I built a cheesy WebGL network sniffeer running in the browser, the basic idea was to build an online collaborative reverse-engineering app where users with the plugin installed can live stream data and everybody collaborates on analyzing it online. Pure crack, I know, but I would personally love to have such a tool).