The main problem with guitar cases it the shape. They don't stack well, and get left till last on the baggage trolley, then thrown on top. The trolley then zooms off at high speed, and as it goes round corners, the small odd shaped bits on top slide off. That's what happened to mine, and the next trolley in the train ran over the head of the case. Luckily it damaged the case, and somehow missed the guitar PHEW!!
The best thing case makers could do, is make a case with parallel sides, and coated with a non slip material.
I have seen aluminium cases like large attaché cases, but only for electric guitars, but while they stack OK, you still have the slippery aspect of polished metal.
I'd like an oblong carbon fibre case with hard rubber edges, but it would cost a fortune.

Giok