IMHO, I don't see test cricket being played in Pak in the next 10 years. if t20is which last a couple hours are played with such caution I don't know how test matches, that are 5 days long will be played. Would security be observing for five whole days.. heck idek if they would wanna watch for that long t20is sure. Forget about observing their duty is to guard the stadium which isn't going to be ideal for 5 days straight.
Also, I don't think inviting teams every two years is very helpful to the cause. itni mushkil sai tho bulaaya jhaatha hai. I'm not saying it's pointless but other teams could think teams like Zim and World XI were just lucky to come back or they might not even care about those teams. I think a major step, in terms of calling teams over to play in Pak, would be to call a top nation. India is obviously not going to come and chances are England might not either. But if teams like SA and Aus pull through that I think would be a boost up to other teams.
Otherwise, the reason I said 10 years earlier is because I only see full series being played in Pak is when the security drastically improves and Pak is not known to be a dangerous place anymore. Be in a cricketer's shoes and think of the mental effect to the cricket world when SL was attacked. Getting attacked is one thing but some players got injured as a result as well. Hopefully iAllah that Pak does become a better place for people and I do hope that I am wrong and teams will start visiting again, but I'm giving my opinion.