Is there a good etymological reason why the potential form in Japanese requires the が particle?
When dealing with the -たい suffix, which also requires the -が particle for what in other languages would be its object, I always conceptualised the word before -が acting as the subject of a "passive desiderative". This might actually historically be wrong (I am not sure), but it made it seem much more logical in my head.
So 私は寿司が食べたい then translates conceptually into "as for me, sushi is desired to be eaten", or changing the form into an adjective (which the -たい form kind of is): "as for me, sushi is desirable for eating". Thus "sushi" becomes the actual subject of the sentence, and the が particle becomes logical.
Now I am looking to see if it is possible to find a similar explanation for the reason why the が particle is used for the potential form… I can of course simply see the potential as a passive (quite logical, as the forms are identical for -いる/える verbs anyway), but that leaves me with a different meaning (e.g. "as for me, Japanese is written", rather than "I can write Japanese"). This would only make sense if the potential meaning directly derives from an earlier passive meaning, which I am not sure of.