Newby here. We’re evaluating Discourse as possible successor to our SMF forum. Performance of the iOS/Android app is crucial, because members of our club are currently fleeing into ad hoc Facebook and WhatsApp groups.
I installed the Discourse app on an iPhone wit iOS 11 and an Android 7 phone. I’ve seen how you can upload an existing image or take a photo to include in a post. That works great. But I know many people work the other way around: They are in there camera- or Photo’s app, decide that they want to post a picture and tap on 
(iOS) or 
(Android). This opens a list of apps available to share the picture. Not only the OS-native apps like Mail and iCloud, but also other installed apps like Signal and Outlook. But I’m not seeing Discourse app 
Did I miss a setting? Or should I turn this question into a feature request?
But you got me there. I must confess I did not think of our members ever subscribing to another Discourse based forum. But that could happen if Discourse gets popular here in the Netherlands. I can imagine that with multiple forums in the app, it would require extra code to create a “please select a forum” step. With just one forum, I would expect it to open with an empty “create new topic” and the picture already in the message body.