Hypercube modular hotend mount

I tend to change the hotend to experiment on different materials & settings and even on different hotends.
So I decided to design a compact, modular hotend mount.
Another requirement was to keep it j-Head / E3D / Immaginaecrea compatible while requiring only minor Z adjustment.
The fixed part holds a blower fan, the single module is a classic two-part holder for hotends (which in the case of j-Head adds a press-fit for bowden PTFE tube) which may have the 30mm fan support, depending on hot