Allow editing of edit summaries in some circumstances, for example if the edit is both your own edit and last edit, and the edit happens recently.
This card tracks a proposal from the 2015 Community Wishlist Survey: https://meta.wikimedia.org/wiki/2015_Community_Wishlist_Survey/Miscellaneous#Technical_user_right_to_edit_summaries
This proposal received 43 support votes, and was ranked #19 out of 107 proposals.
Original 2008 description:
I propose to implement a mechanism to correct edit summaries (1) if it is your own edit (2) and if it is the last edit (3) during a short time span (e.g. 1 - 12 hours).
One possible way to do this would be a link on history pages, e.g. "(rollback | undo | fix summary)". A new page would then allow to fix the summary.
Such a function would allow to fix accidents such as empty summaries, switched summaries (when you have many tabs open), and half-completed raw summaries. Currently, minor or fake edits are required to provide a correct summary.
Under the proposed restrictions (own, last, recent), there is probably no potential for abuse (e.g. any following edit would make the previous summary permanent). This would allow to simply overwrite the edit summary field without the need for a summary history or log.
This might have to be restricted to registered users as theoretically an anonymous user with reassigned IP would be able to change summaries not belonging to him.
There is a current  Village Pump proposal (https://en.wikipedia.org/wiki/Wikipedia:Village_pump_(proposals)/Archive_30#Being_able_to_edit_your_edit_summaries) with currently only positive responses.
There is a also somewhat related closed bug T12105: Allow editing of edit summaries after the fact which did not discuss reasonable restrictions or implementation details. The current proposal addresses previous objections such as increased user interface, system, or code complexity.