Dear Pablo,

Dear Christoph,

just in case it might help to your meditation.

First of all, lpaths are XPath implemented with Lua in ConTeXt.

XPath seems to have as it primary purpose to address the nodes of XML trees.

About your sources, the real issue here is to define whether you want
TEI or TeX to be the format containing them.

I mean, if you add explaining footnotes to your TeX file(s), XML won’t
be source anymore.

If you don’t want this to happen, you have to encode them in the TEI XML
sources.

In my case, the connection to the original source will be lost.  While we will still try to backport corrections, the connection will be lost at the very moment when we will annotate the source text.
From this point of view, an independent source is created here anyway, so I have the freedom to choose between TEI or TeX.
At the moment I'm leaning strongly towards TEI, also because I could try to remove the annotations via XSLT once the work is complete, diff the result with the original source and improve it). And besides, XML+ConTeXt looks quite elegant from the distance of my ignorance. (Although reading xml-mkiv.pdf creates a pleasant frictional heat in my cerebral convolutions, but leaves at least as many knots in them as XML data have nodes).

One last suggestion about proofreading. This is something I learnt from
personal experience.

The first reading is much better to catch errors in the text than the
subsequent ones.

Having the text properly formatted and printed on paper helps a lot to
spot errors.

Same here: It's the paper!
(I for myself prefer for the first proof reading a page lots of white space, in monospaced font like Courier, while my proofreader wants to see the font that will be used in the end.)

Thank you very much for your suggestions, 

Christoph