Beyound the reach of the terrorist organisations? We have already seen pretty sophisticated operations by relatively small crime organizations (like exploiting pseudorandom generators in casino slot machines). There's an established black market for exploits. I think writing an end-to-end encryption app is not much more difficult compared to this. What's more, it will even be perfectly legal in many countries, meaning you could legally hire professionals to do the job. Terrorist organisations won't need to esablish a development office in SV to write the app, they will only need to know how to use Tor and wire money to the app producer. Which isn't such a huge competence to ask for.