Create a badge which rewards viewers with the longest consecutive subscription. These "Longest Streak" badges would appear like the current Founder badges, and reward viewers who either:

A) Met a certain threshold of consecutive subscribed months, and/or

B) Ranked within the top 10 longest consecutively-subscribed viewers
(top # could be modified and scaled with the size of the streamer)

This badge concept would reward those viewers who maybe weren't lucky enough to find the stream early and get a Founder's badge, but still have been consistent and unwavering in their support of the streamer they love watching.