I tested a concept iteration over array in format [key1, value1, key2, value2, .. ] - what is nice, it works for [[key1,value1],[key2, value2], ...] too
It is only a few lines more to current code, and this change doesn't break a compatibility.
If we're going to go that route, I think it makes more sense to create an actual key/value type (ie: http://pgxn.org/dist/pair/doc/pair.html) and return an array of that.