Jon,
you're right in that I don't play much matchplay. But in the 55 matches that I did play (35-18-2), the good-good situation has never once come up. I give putts immediately and so did all my opponents so far. Never once did I encounter someone, who made me stand over the ball or even just mark it, only to concede the putt then. Frankly, that would have been quite off-putting to me.
There may have been a situation or two, where I let my opponent mark his ball, because I was standing too far away from the hole to judge whether it was a missable putt or not and then later concede it, when I got there and saw it was close. But again, it's still a case of me giving a putt and expecting nothing in return.
So if you frame it in that context, you can clearly see that the good-good situation can practically never come up for me. If it's a frequent occurrence in your matches that two markers are close to the hole, then it's a different game from the one I play. You may well be right that in your game a good-good is practical.
Ulrich