If I understand correctly, the caller of get, put, del, etc. is *always* another cfs package, correct? In other words, no "end user" provided callback is ever burrowing all the way down to cfs-gridfs, right?  I think it's fair to say that the previous "gridFS-like" implementation of cfs-gridfs is the *only* conceivable implementation of an SA that *wouldn't* need to use-non Meteor code. That is: the only way to implement an "all-Meteor" SA is to somehow stuff the data into Meteor Collections.
My point being: all useful SA implementations will be non-Meteor code (it's not really a "choice") and since user provided callbacks will never be seen directly by the SA code, the `Meteor.bindEnvironment` wrapping should happen outside of the storage adapters in one place, rather than requiring them to each be fiber aware.