As a daily user of the Amersham branch trains, I'm keen to see the arrival of the S stock. Although the trains will have fewer seats (and no sign of an increase in service frequency until signalling upgrades are complete in 2016) I think the new layout will make getting on and off the train and standing (when necessary) a more pleasant experience.
Unfortunately even North of Harrow on the Hill it's often necessary to stand during the morning peak, as it's also commonly the case heading out of town in the evening. The A stock's 1 1/2 and 2 1/2 seating layout don't make for very comfortable journeys when the train is full as you're either squashed against the wall, in the middle, or hanging off the edge of the seat.
When TfL ran the mock-up S-stock at Euston a while back, one of the project people said that if you regard currently Met Line seating as 1+2 then the new trains will offer a similar number. Yes, a diplomatic way of selling fewer seats but I appreciate the point.
I've also thought about the prospect of Chiltern taking over the Amersham branch services (not that I believe it's on the cards). However the problem I see with this is the capacity limitations into Marylebone. Even with 4 trains an hour (2 currently being fast to Amersham or Great Missenden) the current Met-line stations would notice a significant drop in capacity. Given also that the stations can only cater for 5-6 cars, capacity would be a real problem for this prime commuting area.