Interesting proposal and I like it very much since an outsider is no longer keeping any BNT due to triggering the vortex. This brings it internally to the protocol and prevents leaking any BNT to outside entities. Note that the vortex fee is either 2% or 100 BNT (whichever one is lowest) per the recent proposal:
that was passed.
In B3, the vortex trigger is supposed to be an outside initiator or a keeper job. If the DAO can fund the keeper job using the fees that it gains from triggering the vortex then it should be a self-supporting system. I am assuming that we can set this on a schedule to run based on some frequency which we deem to be OK. Note that the bancor 3 vortex is not yet ready but I just wanted to throw this out there as it was part of the vortex b3 implementation.