Increasing the max size of replica sets with non-voting members

I would like to build a replica set which allows local reads in more than 12 locations. Limiting the set of potential primary nodes to 7 would be fine, but it would be helpful to add a large number of of nodes with priority:0 and vote:0 nodes (no participation in election, and no possibility of becoming primary) in order to benefit from the replication process across a large number of locations.