Collectors update redux

[Brian Goetz]

> I think there is *way* too much stuff in there, and I don't have enough
> time to even review it all before it gets set in stone.

"Too much stuff here" is kind of vague.

Is the concern that some of the operations (e.g., partition) are just 
too niche to carry their weight?  Or not fully baked as concepts?

Or are some so obvious that we just expect people to write it themselves 
if they need it?

Is the concern that there are too many forms of each operation, and that 
the user will be bewildered by the variety?

Is it the complex interaction of {concurrent, ordered}?

Can you point to a few examples of methods you would eliminate?  Maybe 
we can induct to a pattern from there.