The killer apps could be mutations of existing, clearnet apps if the developers consider what the users of the app might really want and then take that to the limit, if one no longer has to consider legal boundaries of any sort.
For example, existing apps help people do such things as find a place to live, save money, make money, “get in touch” with old acquaintances, chat with like-minded people.
It might take a while, because there’s tremendous inertia in the existing systems that keeps people doing the same old things and thinking the same old ways even though the accustomed boundaries have weakened to the breaking point: I’m reminded of Wile E. Coyote running off a cliff and taking a few seconds to understand that he is standing in mid-air.
[EDIT] Some examples of my use of the paradigm that I touched upon above, of considering what people want:
People like to watch sport.
As it happens, exclusive rights to televise sporting events are expensive to obtain for conglomerates such as Sky. they pay top dollar for such rights. One SAFE app might be a restreaming service, that takes some sporting event and retransmits it.
Ditto for movies, restreamed one day after their official release.
People are interested in “celebrities.”
A SAFE “media” business might make the average paparazzi seem like prudes, literally hounding celebs to death. The existing mass media like to dabble in that: appealing to the sadism and envy of the crowd. Such a business could make the most lurid tabloid look staid by comparison.
Same for court cases which have gag orders on them.
In fact, you organize a war: Not just the twitter events of the faux, color revolutions. I mean a real insurgency war.