Mr Papa said
what would the smartphone app do???  if you use a responsive wp and sp theme, it will just resize for mobile usage...

  

Using the Facebook app as an example - minus It's data snooping attributes. It's really handy to tap the FBA's icon and be instantly connected. Maybe for a forum it's overkill. But logging in via mobile can be a pita unless using Chrome mobile browser with a saved Google password. At least for me it's a challenge, add a computer generated secure password an it's a nightmare.

Mobile site access has surpassed Desktop some time ago. Google is now ranking websites by how their mobile site performs vs desktop as it used to be. Yoast wrote this ultimate guide to mobile seo article. No problems with SP Reboot theme that i can see. I was just thinking an app would make it easier to use the forum on the go. I'm not a coder but obviously it would have to incorporate a web browser and have predefined linking. Just a thought..