I will link you to an extensive comment of mine on this matter:
The long and short of it is that it's a lot of development effort (especially to keep up with new mobile versions) that we don't have time for. If there was an app, then that would delay IPS software updates even more for testing to make sure nothing breaks. This is to say nothing about the amount of time that would be spent on the app itself, which would be extensive. (We already have a software project, the new WoB Archive, and this takes a lot of time.)
Additionally, I'm still confused as to what the real gains are by having an app and spending that time doing that. The mobile site is very, very good and I use it for most things, including the backend to do administration. Perhaps you can explain to me a use for an app that cannot be served with the mobile site? The only real thing is mobile push notifications, which you could just as easily get with email notifications.
An app would just be a slightly crappier wrapper for the forum and would interact the same. I don't understand why that's preferable to opening the mobile site.