XeTeX support for Tibetan

After a little search, I managed to get the linebreaking algorithm work with XeTeX. I was so happy that I wanted to make it available for Thai too, but it's alreay there and commented with 

    %%TODO \XeTeXlinebreaklocales "th"% uses ICU to find line breaks on the basis of a dictionary lookup-- make this optional? (in case a user might prefer a preprocessor

It seems a bit strange... do users really prefer a preprocessor?