Honestly, if we can't use Tapatalk, I see little point in developing an in-house app. The biggest reason to use Tapatalk was quick and easy access to the rest of your forums, all in one app. I'm sure other members utilized the notifications, but I found them annoying and favored simple email notifications.
But XenForo's mobile web experience is good enough that having a standalone forum app for a single forum doesn't make a ton of sense in my eyes. Hell, on mobile web, you can now embed a photo and adjust its size from within the text editor! XenForo is powerful and I think it can stand on its own as simply mobile web. I won't be ditching the forum because of this, because visiting the site on my phone with Chrome or Opera is good enough. And WORLDS better than doing so when it was still vBulletin.