We need a typesystem-sanctioned way to cast qualifiers away

[deadalnix via Digitalmars-d]

That's only one aspect of the problem? the other side of the coin 
is that you'd like the qualifier to turtle down your collection. 
Right now,

const(Collection!T) is different from 
const(Collection!(const(T))) .

Back to your problem, the only I see to write that in a way the 
compiler won't bite you later is to get a reference to the field 
(refcount of allocator) cast the qualifier of that reference, and 
then manipulating it.

Everything need to go through the casted reference. If you drop 
it and get it back again, the compiler may assume thing you don't 
want it to assume.