Marc:
Interesting question and thread.
Like all definitions on here and in golf and golf architeture in general, the exact definition of a "parkland golf course" may be a bit debatable.
But having said that I really like your mention of Humphery Repton and Capability Brown because I think there's little question what a "parkland" estate is and what it consists of design and landscape architecture-wise.
Therefore, I see no reason to assume that a "parkland" golf course should look in any way different than a "parkland" estate (minus the golf course, of course
).
One of the features of a "parkland" course, in my opinion, is mature trees and vast vistas with loads of mown grass.
By the way, as of now, Merion East has mowed down huge areas of their rough area (although some spots of very high fescue remain). I was over at Aronimink the other day and all the rough everywhere is mown down very low and you can see the architecture and vistas through and under the mature trees.
If any US golf course is representative of a "parkland" golf course it would be Aronimink right now.