>> I'm wondering: I don't really know how the people who want underscores
>> plan to use this, but would it make sense to scope this differently,
>> i.e., either on a per-class or even a per-method basis?
>
> Scoping? Why? A preference is
>    a) simple
>    b) settable by the image owner who is able to decide if he
>       wants to allow it or not (same as with underscores)

scoping makes it possible to load code using selectors with underscores 
in an image where most classes still use underscores for assignments.

I do not see any other way to avoid forcing everybody to review their 
code and check all assignments.

plus, if underscores in methods are mostly useful when interfacing with 
external blobs as Nicolas put it, a per-class scoping makes sense since 
only classes involved with the blob would really need underscored selectors.

so, scoping gives the functionality you want and gives all other people 
confidence that their code won't break. how do other solutions compare ?

Stef