I never use sed -i because I can't rely on that being a standard feature as I move from system to system. With a utility as basic as sed that is found on almost every UNIX (and hence often used in a system's startup or configuration scripts, etc.), I want my own sed scripts to work consistently across all systems I might use.

If I really want to create temp files I can use ed or use sed with shell redirection. Were it for some reason a requirement, I can avoid temp files, at least for the substitution (s) command, as follows:

  sed -a '"$1"';H;$!d;g;w'$2
  where $1 is some sed s commands and $2 is a file

This is not "perfect" as there will blank lines, but it does the job without temp files (if that were really a concern).

If GNU grep was in need of repair and you fixed it, then I thank you. But I'm not clear on how that justifies any "extensions" to GNU grep.

Maintenance, at least to me, means fixing things, not extending them and adding more complexity and things that can potentially break or create incompatibilities across different UNIX's.