i think i am one step closer to my goal.
alla i have is to combine:
1- What Hans taught me about working on file (and not simply stdout) python has already a module tempfile.NamedTemporaryFile() ,
2- Your snippet to run ConTeXT inside the temporary folder cd && contextjit --purgeall --path="%d" --arguments=filename=%d/%e.pdf
--result="%e-2UP.pdf" /home/ousia/A5-to-A4_landscape-booklet.tex
To be adapted for a working example ( tomorrow i have a night shift so probably tuesday i will work on again).