Have a new write concern w:default, which is based on the configuration. Drives would specify this and the server would determine what this means. Having a default write concern that is concrete forces w:1 to account for standalones. This would allow for a more intuitive write concern depending on the MongoDB configuration (not the current state of that configuration).

w:default would translate to:

The argument could be made for Replica w/ arbiter to be half of the number of data bearing nodes as this is static with config too.