Does Bryston have any interest in designing an amp specifically for subwoofers? A lot of good subs are unpowered, and this is an area where a good amp and a good warranty would be appealing.
I expect I don't need to tell folk at Bryston how to drive speakers, but what I'd look for in a sub amp would be:
Efficiency - No need to run up an electric bill for a subwoofer.
Price - this application is not as demanding as some; so no one wants to spend thousands on a sub amp.
Cleanliness: +/- 0.5 dB from 0.5Hz to 250Hz, THD well below 0.1%
Ability to drive 1 ohm loads with aplomb. (eg, Ability to drive a *pair* of subwoofers gracefully, as this is useful in big rooms.)
Small form factor - someone might decide to put it inside a sub, or mount it on the sub.
Very vibration-proof and magnetic field - see last point.
Ability to turn on and off via a 12v signal line, plus auto shutoff if idle for a few hours.
Big number wattage - 500W into 4 ohm, minimum.
Bryston's typical S-to-N of "N? What N? I don't hear any N."
Absolutely no mechanical hum (subwoofer enclosures could re-resonate even minor hum in an annoying fashion)
And my favorite: 20 year warranty.
Taken together, I think there's enough technical challange here to make this interesting to Bryston engineers.

Bryston's stuff is built like a rock, but the prospect of 150db@0m shaking an amp non-stop should push the envelope a little. And 1000w at *1Hz* with a THD 0f 0.05% and StoN below 110db, at a significantly lower price point than a 7B, probably isn't trivial...