(*My own Machi definition)
Should a girl machi with a guy? or the other way round? If both have same favorites, can considered to be machi. If suitable maybe can developed to in a relationship. However, mostly cannot, a lot of problem will happens if machi developed into relationship.
In my opinion, this machi is doesn't matter. It is just like bromance, isn't it? As long as two people like to get along each other, there is nothing wrong with the gender.
Do you have machi right now? Quickly get one and make your life meaningful then ^^