I'm finally getting up to speed on Ionic 2 by working my way through the excellent book "Building Mobile Apps with Ionic 2 from Josh Morony.
I've been pleased to see the Ionic Team created a build process so your code is completed in /app and the output is generated in /www. This will replace my previous custom build process when working on Ionic 1.X apps.
I like how the gulp process uses imported scripts to handle the copying of HTML, JS, etc. This keeps your Gulp file from becoming overloaded with JS and makes it much easier to read. They even have a handy Github repo for these simple build scripts.
In Josh's book, he suggests keeping image files in the www directory. For me, I'd rather have EVERYTHING in the /app directory and nothing in the /www directory for version control purposed. This way, the entire /www directory can be ignored. This allows one true source of all app info.