Killer app would be something which allows you to trade in the exchanges without losing all your coins if they get hacked. That'll bring confidence back to crypto 
Are you talking about MGW and uMGW of NXT?: http://multigateway.com/
All the info:
https://nxtforum.org/nxtservices-releases/how-to-test-multigateway-with-nxtservices-a-test-user-guide/
We talked a bit about it few pages ago :
https://bitcointalk.org/index.php?topic=624223.msg7985996#msg7985996
https://bitcointalk.org/index.php?topic=624223.msg7986586#msg7986586
It's cool! Can't wait to have more alts and maybe a USD market
I can't believe features like MGW and Blackhalo isn't famous yet