I would pay an additional license fee for a XF mobile app, especially if the app was designed in a way that made it possible for plugin developers to tie their plugins to the app somehow (not a developer myself, and I know I'm oversimplifying it) - I'm referring to apps like Showcase by @Bob
and others that are made for content. I am a big believer that forums need to evolve in a way that includes not only push notifications, but also allows more content to be shared directly from mobile devices, and soon.
If your forum members take photos using their phones, where are they more likely to share those photos? The road blocks and extra steps it takes to open a browser on the phone, navigate to your forum, click around and find the right place to post the photo in the forum, and then use the upload feature to click around and locate the photo on the phone can take WAY more time than clicking the Share button after you take that photo and selecting FB, knowing that some of the people in that forum are friends with you on FB anyway. Why go through the extra hassle of also sharing that content in a forum?
For some communities - take the car enthusiast communities for example - those photos signify what that member is working on at the moment with their car, and that is an extremely important community-building element that is starting to drop off in forums these days. People will share what they're doing with their cars on FB because it's FAR easier to do. I'm sure this is not a problem that is exclusive to the automotive community.
I've been talking with members of the site for several months about this, getting their feedback and taking notes. The consistent message coming back is that the forum will always be a great place for finding technical information, but that FB is becoming more preferred for engaging and networking with other car enthusiasts because of how simple it is to use, especially on a mobile device. And being a technical resource only is not going to keep a forum community thriving. 65% of my traffic views the site on a mobile device these days. I'm using a mobile friendly theme without Tapatalk (it doesn't work with many of the plugins on the site that set my community apart from other car sites). I would LOVE to have an app that is built by XF and made specifically for XF and can be extended by some of the talented plugin developers we have in this community. I'd pay an upfront license fee and a monthly fee for that.