Hello Oasis;
I think this is an excellent idea, and one that Bang & Olufsen could pursue. I would be easy enough and would serve to protect the looks and function of the BS 3.
In taking the original " portable " Beosound 1 here and about, and having scratched two BS 1 grille covers over the past 5 years, you take chances with your investment. Replacement grilles are not an inexpensive item at Euro 175 + each, and some of the original colours have since become unavailable.
The two that I purchased in Europe were later taken to North America and then on to South America. I cut 2 " thick Coolite (blown cellular styrene) foam into 4 patterns, and taped the sections over each BS 1 to carry it through as accompanied baggage. I did this as it was somewhat double safe inside a locked suitcase, than inside the original B&O carton alone. Also less obvious considering theft these days.
This method works, and would also for the BS 3, but can be a bit of a mess at times opening and closing the packaging when taped. A good carry case, padded on the inside, and bottom, could utilise the BS 3 carry handle at the top. Until such time as B & O offers such protection, you might want to onsider the merits of using one of the Pelican Box models available in Sailing or Diving shops. These are light, water and dustproof, and thickly foam-lined. The foam inside pulls out, and can be cut to fit a BS 3 plus all cables, cords, and other accessories.You can see one of the cases here: