Thanks Luigi!

It turns out that with some slight modifications I could typeset the mentioned project with mkiv. 

Then after having added the following from your article:

%% For PDF/A

\setupbackend[

format={pdf/a-1a:2005},

profile={default_cmyk.icc,

         default_rgb.icc,default_gray.icc},

intent={%

ISO coated v2 300\letterpercent\space (ECI)}

]

%% Tagged PDF

%% method=auto ==> default tags by Adobe

\setupstructure[state=start,method=auto]

I could get a PDF which looks fine: but now I have to make sure that it is PDF/A compliant.

Right now I don’t hav etime to check this, but in any case you gave me good hope… Thanks!