Joseph and all,

    https://www.dropbox.com/sh/mh8c67bxidryr8h/AAAu4_Ez66syXyKwL3J83nn_a?dl=0

I finally had a chance to look at all this work.  Very nice.  I didn't
do a test install of it, but I don't expect any serious problems that
way.  It would be helpful for that purpose if the .tds.zip files were
available as their own downloads, but anything can be made to work for
testing.

The only question that I have for now is whether ltunicode plus your
other changes are intended to exactly replace everything that was in
unicode-letters?  That is, was there anything known in unicode-letters
that is not now provided in the new LaTeX2e?  I know you have the
new .ini files without unicode-letters, but I thought I'd ask explicitly
anyway.

TL will still need unicode-letters for the plain lua+xe formats.
Therefore it would be good to be in sync :).  I gather you generated your
files from what is now at http://www.unicode.org/Public/UNIDATA.  (I tried
running ltunicode.dtx with etex and got exactly your ltunicode.ltx.  Yay!)
I will regenerate unicode-letters.tex (which is a bit stale) from that
data as well for the pretest.

To help in this, I wonder if we both might include somewhere the exact
file sizes, or something, of the three data files used in the generation
(UnicodeData.txt EastAsianWidth.txt LineBreak.txt).  E.g., just in the
comments in ltunicode.dtx.  That is the simplest "version" number I can
think of.  I'll change the unicode-letters.tex stuff in this regard, at
least.

Thanks for all this work.  I both fear and look forward to trying it
for real :).

karl