I misunderstood your earlier post. I meant to say that two-handers have both a foregrip and a rear grip and the double grips might come in handy for fighting big fish. I see now you were making an important point about leverage during long battles.
As far as what would change, (in so far as my opinion on this matter goes) there would be a rear grip added below the reel seat. The action of the rod would be such that it accomodates the increased stroke speed of two-handed casts, and it would generally be a little longer which offers a distance advantage when two-hands are applied. But not too long - the traditional Spey rods are up to 16 ft long and made with a sweet flex point in the heart of the blank to help swat huge amounts of double taper belly up river banks using contrived roll casts. I believe the modern SWFF two-hander should not exceed 12 ft, no reason for it if the blank is designed for overhand casting.
The line management of running line changes in that the line hand is occupied with the rod, but it shoots just fine out of the basket.
Hey I've got an idea - I'd love to bring down a few of the doublehanded rods to see what you think. Let me know when there are some fish around and I'll swing by. The rocks at the Nobska sounds like a good challenge.
I hope we're still on for some "field testing" of these rods when the big stuff arrives