> for example it's possible to check out only the relevant sub-tree from the remote, or to commit changes only to the said sub-tree w/o having to affect and therefore contest the history of unrelated parts of the repo.

I'm misunderstanding your statement... are you saying it is possible to do this, or you would like it to be possible?

I am looking for something similar; I would like to archive a bunch of data, much of which is binary rather than text, in a hierarchical form, and work with subtrees without having to clone the whole damn thing.