[XeTeX] ATSUI/Core Text/etc. Re: "Minimalist" TeX?

[Simon Cozens]

On 19/05/2012 03:22, Mojca Miklavec wrote:
> I might be wrong, but I think that currently a much more awaited patch
> would be one replacing ATSUI library calls with Core Text. I guess
> that would be way less work than replacing PDF library and bring way
> more benefits to the community.

I'm coming very late to this party but could someone explain why Core Text 
would be the best replacement here? It seems like swapping out one OS-specific 
library for another, when there are platform-independent text layout libraries 
available that could be used instead. (I don't know any XeTeX internals yet so 
I don't know what it uses on non-OSX platforms already.)

Why not replace ATSUI with e.g. SIL graphite or Pango/Harfbuzz?