little reason to continue even with XeTeX.
Just for the record, even in the hypothetical future where LuaTeX has
caught up to XeTeX in terms of system font access and Arabic
typesetting, Jonathan K once spoke to me about another reason why XeTeX
will very likely always have a place: good typesetting of other minority
scripts. Since everything in LuaTeX is being programmed from scratch,
it seems highly unlikely it will ever support the variety of scripts
that ICU et al. do.