And it's not just about writing "Portal apps", we want every app that runs on Portal to also run on competing personal cloud server platforms. That's what true decentralization requires.
The biggest difference is that it looks like you have people include a script to install the app, and Sandstorm packages the app and all it's dependencies 'pre-installed', and is mostly independent of Linux flavor.
Since Sandstorm packages have all the dependencies and app data in read-only, and all of the user's app data in /var, I would think it'd be relatively possible to figure out how to get the two formats to play nice.
For now, we're just trying to keep it really simple and the JSON config seems as simple as we can make it. Apps could do a lot more, like include their own OS images or rootfs tarballs if it makes sense.
Though running individual Sandstorm apps as individual Portal Platform apps is probably also doable, since SPKs contain everything a Linux server needs to run an app. Sandstorm and Portal Platform manifests are pretty similar, and the way the apps are run are similar.
My thought here is just that if your 'install' script can unpack and set up from an SPK file, you might be able to take advantage of some of the apps already being published (currently) exclusively for Sandstorm.
I've been poking around Windows' SDKs to turn iOS and Android apps and stuff into Windows apps, so the concept of this sort of thing happens to be fresh in my head currently. :D