Access visibility and linkage

[Arun Chandrasekaran via Digitalmars-d-learn]

I was reading through 
https://wiki.dlang.org/Access_specifiers_and_visibility#What_is_missing

There is currently no way in D to mark symbols for internal 
linkage, saying "this an implementation detail, you should not 
even know this one exists". This is an important module-level 
encapsulation tool which also somewhat guarantees that those 
symbols can't be linked to by accident by some other module and 
you are free to change them keeping binary interface same.

DMD v2.077.1 exhibits the same behavior. Is this is already being 
worked on? Or is there any plan to address this? Can this be 
fixed? If so how? If not, why not?

Name clash between public and private symbols has also been 
stated as unneeded and useless feature that makes possible to 
break a compilation of a project by changing private name. It 
is also impossible to use an UFCS function now if class already 
has private one with same signature.

Also, why is the default visibility of global variables at module 
level public Shouldn't they be private by default to provide 
better encapsulation guarantee (and linkage guarantee if the 
above is addressed in future)?
From readability point of view as well, for instance, if I want 
to know all the functions "exposed" by the current module, I can 
simply grep for public.