3rd Party Authentication
Enable login with popular sign in options like Google, Facebook, or Twitter; or connect your Users collection to a 3rd party API that supports Oauth authentication.
Instead of manually clicking the "Send" or "Enter" icon, user should be able to hit the enter bar. This affects creating accounts and other areas.
Horizontal List Component*
View items that can be swiped horizontal to see the next item. *Note that there will be two versions of this component. One will be Horizontal Lists (or Tiles) that can be swiped continuously to see the next images much like Hulu, Netflix, etc. And the other will be a Carousel List component that will take up the full width of the screen (so you only see 1 at a time) and will display the dots underneath the image so you can see how many photos there are much like Instagram images.
Proper dev/test/staging/prod workflow
Need a Git-based workflow that allows one to safely do development without breaking the live app. Should allow one to make structural changes in collections, add/modify screens and add/modify data without breaking anything. Then be able to port dev changes seamlessly into production app. Take a look at Pantheon's dev workflows for ideal UX.
Notification type: Web hook
It would be amazing to have a new notification type called "web hook." So instead of generating an email, SMS or push notification, you could trigger a post hook to a specified URL with whatever payload params you want to send (similar to building a message). Zapier or Integromat can receive those post hooks and handle the rest from there. This is a feature that would pay compounding returns...
Stripe - Marketplace Payments for Subscriptions
Enable marketplace payments for Stripe subscriptions (the same way that single purchases are).
It would be great to be able to access the users location in order to filter for location specific content. For example local events or classes etc..