There is lively.el [1]! It is also on MELPA in a more recent version [2]. It allows to put an elisp expression into any buffer and then replaces that with the output in a time interval or manually. I use that frequently.

[1] https://lukego.livejournal.com/23379.html [2] https://github.com/purcell/lively/tree/348675828c6a81bfa1ac3...