I personally like the simplicity of roller blinds, especially since they're almost invisible when "up". That means that they don't detract from the great "open" expanse that a sliding stacker creates. But, they obviously have their negatives since they couldn't be down if you wanted the doors open for breeze/airflow and you'd probably need to have more than one blind open at any time since multiple rollers would be controlled by a single cord/chain. Sheer curtains and sliding panel blinds can also look nice. I'm not such a fan of these, as they need to be "bunched" at one end (or both ends) and they obscure the visual appeal of the sliding stacker doors. If you had enough "wall" space at one end of the sliding stacker door, then you could "bunch" them there. Here are some examples/suggestions:

stackers open up wider but glass doors are quite heavy so suggest more narrow panels rather than less wider heavier sliders...if planned in advance the bottom tracks can be recessed into a suitable floor to reduce trip hazards..we have three stacking panels with an extra matched height section with an awning window for ventilation when we don't want to open the door and/or in bad weather..the doors and window are connected into one tall wide section of 4 equal sized panels..Given the ideal situation i would also have window sections across the top for extra height and include electric openers that we have used elsewhere and find are very useful for opening high windows without having to climb up something to reach

although i always prefer curtains a 6m wide opening will need either a very light fabric or about 1 m either side to fully pull back to each side where blinds would be able to be raised completely above the window (assuming there's somewhere to attach them) discuss options with a window covering specialist as there are some new options that may suit you better..i also suggest to clarify flyscreening, security and ventilation options for your very wide opening as we found a more flexible and cost effective result with a door height panel of stacked awning windows next to a wide section of stacking doors so that we can open the window for ventilation without opening the doors

That's a hard one. My initial thought was to pop a roller-blind above the stacker doors, (that's what we have done and it works well) but with no other blinds in the room this may not look that good. What about drapes that hang on either side of the stacker doors - is there room? Can they be hooked back somehow to the side? This would add a softer element and introduce a new colour or texture that would look lovely with the plantation shutters. Hard to comment further without a photo.