Lack of good binary support for transfer, internal use, and internal
storage is a huge killer for JS, IMHO.

Perhaps.  However, I'm having a very difficult time getting over my amusement at being told that efficient data types for binary data are critically important on a list devoted to XML.

"Laugh while you can ... " :)
Yes I agree its amusing, but in the mobile space (which is really yesterdays desktop space ... and tomorrows 'your space' ) getting huge amounts of XML to devices is seriously painful using text protocols.