Custom React Native / React web plugins
Make it possible to add a custom React Native / React web plugin via a GitHub repository, so that the plugin also tells Composer the view components / flow functions / required build service settings it provides.
Support in-app purchases
Add flow functions and necessary Build Service configurations to support in-app purchases.
3rd party auth
Flow functions that would implement 3rd party auth tools (Facebook Google, etc).
Advanced navigation configurator
The upcoming navigation configurator will give users full control over navigation, from full styling of the autogenerated navigation elements to defining things like soft tabs on the page level, as well as customizing navigation individually for different form factors and devices.
Expose more native interaction events
E.g. different swipes, long press, plus the many web events such as onHover.
Custom domain names for web app deployments
Allow custom domain names (e.g. www.myapp.com ) to be set up for app deployments via the Build Service, including SSL certificate setup.
Ability to copy/paste pages, components, etc
One thing that would make development must faster is the ability to copy and paste objects such as complete pages, individual components already on forms, data sources, etc.
UI component/design import from Sketch / Figma / Adobe XD etc
Make it possible to import full designs or individual components from the popular design/prototyping tools into Composer.