obs-service-sed is useful because sed is restricted in how it interacts with the host system. However, editor support for writing complex sed programs is limited. AFAIK, emacs's sed-mode is it. However, that support is still limited - e.g. it does not support extended regular expression syntax. It does not support the GNU extensions to the a,i, and c commands to use the text following whitespace on the same line.
So this repo is for my enhancements to sed-mode, whenever I get around to them. As the author of sed-mode notes, needing to use sed-mode indicates possible derangement. Except for applications like obs-service-sed.