When can we expect mobile app?

According to the road map beta version of the mobile app is released in March, the app will likely appear after the end of the sale.

Will app be available on all mobile OS's?

Android for shure, don't know for iOS according to latest issues....

Internal issues or something regarding restrictions iOS has put on ICOs?

As far as I know those issues are regarding ICOs.

I think they haven't changed their policy around this and probably won't change it anytime soon which is too bad.

On the one hand, it's bad because projects only have one option, but Android is very well represented, so there will be plenty of users.

Android is the most wide spread, but also has wide variety of devices.

So, coverage will obviously not be a problem, the difficulty in working on some devices is something that all developers encounter...

Yes good optimization is the key in that case.

That's why BETA is used to maximize optimization of applications.