A couple of of Lisp hacking sessions later and I'm happy enough with mojo.el to bump the version to v0.9. I've checked off what I feel are the most important checkpoints on the webOS Internals comparison of editors and the framework is in place to make implementing most of the remaining commands very trivial. I might take a bit of time today to flesh things out just to check more points off so people feel more confident that it's a fully featured environment, because it certainly is.
It now requires json.el in order to parse appinfo.json. json.el might be included with Emacs if you have a very recent version, otherwise you can google for it or get it from my config file repo on github where you can also find my latest version of mojo.el. You still just (require 'mojo) in your .emacs file.
The wrappers around Palm SDK commands now search upwards for the Mojo project root directory (from the default-directory for current-buffer) and parse appinfo.json to give you sane defaults for mojo-package, mojo-install, mojo-launch, mojo-delete, and mojo-inspect. You can list installed apps and when entering app ids there is completion and history, as you have come to expect in Emacs. The most useful command for development is mojo-package-install-and-inspect which does exactly what it says: packages, installs, and launches the application for inspection. No interaction is required as long as you are editing a buffer inside your Mojo project.
If you read the install instructions in mojo.el and decide to setup some keybindings then you will have single-task commands for packaging, installing, launching, or all three steps at once.
Please give me some feedback if you try this out. I've developed it on Mac OS X and Jonathan on Windows so please try it on Linux and send me a patch or even better a pull request on github if it needs some work. There is room for improvement. The next feature on my radar before I would consider it worthy of a v1.0 tag is intelligent switching to corresponding buffers, e.g. mojo-switch-to-view, mojo-switch-to-assistant, things like that. Basically things I miss from the Rails package for Emacs.