This has been implemented in Crosswatch. (https://meta.wikimedia.org/wiki/Crosswatch)
It should be incorporated into Special:Watchlist too. It is revolutionary, and will make it easier to edit more. If editors can edit more in the same period of time, then that can help maintain the number of active editors (5 or more edits per month):
--Timeshifter (talk) 18:01, 19 November 2015 (UTC)
This card tracks a proposal from the 2015 Community Wishlist Survey: https://meta.wikimedia.org/wiki/2015_Community_Wishlist_Survey
This proposal received 8 support votes, and was ranked #72 out of 107 proposals. https://meta.wikimedia.org/wiki/2015_Community_Wishlist_Survey/Watchlists#Dropdown_diffs_of_last_edits