Expectations of reviewer activity

Does the wayfarer team have any kind of expectations or visions for the "lifetime" of a reviewer's activity? Is the average reviewer to keep at it long term? Are the badge tiers viewed as a sort of typical ceiling on most people's involvement in terms of nomination count? How many total nominations and at what frequency does the team expect or estimate the average person will send in?
Comments
What comment would Niantic have for a one-off reviewer? A weathered champion? Somebody who reviewed heavily to pass a few dozen upgrades and then quit because there was no longer necessity?