Initially I thought you were talking about Spectre,
and I had to actually read that thread carefully to understand that in the places where they refer to 32-bit being susceptible, they are referring to Meltdown, not Spectre.
The way it was worded it really wasn't obvious, but this makes it clear:
> Many of us are concerned that we are running 32-bit systems that are
> still vulnerable to meltdown;


Now, back to our AMD64 processors...
Is it possible to access/exploit 64bit-specific instructions and features, through a 32-bit OS? That is the question.
We need to find out if some of these features that Spectre relies upon, are still active/available when running in 32bit compatibility mode for a 32bit OS with 32bit software.