It's taken how long now with a number of promises and delays so I'd be surprised to see a 6" in a high frequency. More than likely a 7.5 kHz 6" in concentric and Double-D designs .... if that.
I had hoped the 3 kHz operating frequency would help give the X-Terra an 'edge' in our higher ground mineralization when going after some deeper (5"-8") silver coin, but it didn't cut it. Absolutely no challenge for some of the other models I have used, and especially no threat to Minelab's own excellent Explorer II or SE for serious "$ilver $hooting."
The High Frequency coils showed me more potential, but mainly if I wanted to concentrate on hunting gold jewelery or possibly gold nuggets. Overall, however, the best performance I got at a variety of site environments around here (NW Oregon, Eastern Oregon and elsewhere) was with the 7.5 kHz frequency.
I just don't care for the very open coil designs or bigger coils when hunting ghost towns or the overgrown parks and other sites I hunt that abound in short, stiff brush.
I think a 6" concentric coil of solid design operating at 7.5 kHz is not just seriously needed, it is long overdue!
Monte