OS7 is OS6 with pretty icons, its like taking windows 7 and installing a new theme and calling it windows 8.
QNX which would technically of been called BNX if RIM did not run into trademark issues using an already registered name is only due q2/q3 next year. So making an app for os7 is no more difficulty than os6, you just need to adapt to new screen sizes, same thing with BNX, its an open ended os said to support every known programing language, in theory it should support BB, droid, ios, symbian, winmob and j2me apps with minimal tweaks that RIM will even do for you at no cost to you.
Problem is more likely that current OS uses an exclusive language that is vastly different to anything android and apple are using, its like its their own private code and thier app requirements to be allowed into the app store are immense. MyBB is modifying the vbulliten for the forum, they not actually building their own up from scratch, if you really want a MyBB specific app you can just buy a copy of TapaTalk and you will be sorted. They provide it for android and ios cuz it costs them $99 a year, for berry they would have to go and develop 1 from scratch with is financially a complete waste of money.
$4 and you will have a ful "MyBB" app for your berry and better yet, you will be able to access thousands of other forums at the same time.
Besides if you have a look at the droid and ios section the MyBB app has so many complaints, works on so few devices that people have simply gone and spent the R20/R30 for the android app, not sure the cost for the ios one. As far as users of those platforms are concerned the MyBB modification app is a complete disaster. Chances are anyway you use more than just MyBB so the $4 will more than pay for itself in usefulness when you can access all forums ont he move with push notifications for new posts/pms/etc.