The general problem of indexing attachments requires some help to turn
things into text, but (most?) text/* should be doable internally,
possibly with optimizations as for the text/html case.
The corpus is not really suitable for general indexing test since the
sole message is ignored (and will most likely continue to be ignored)
by notmuch-new.
This particular message is not recognized by notmuch as mail, but is
fine according to e.g. mutt. The trigger for this bad behaviour seems
to be a second "From " ocurring at the beginning of the line but
inside an attachment.
