I am writing an editor which has lot of parameters that could be easily interacted with through text. I find it inconvenient to implement a separate text-editor or lots of UI code for every little parameter. Usual buttons, boxes and gadgets would be burdensome and clumsy. I'd much rather let user interact with those parameters through vim.
The preferable way for me would be to get editor open vim with my text buffer. Then, when one would save the text buffer in vim, my editor would get notified from that and update it's view.
Write your intermediate results (what you want the user to edit) to a temp file.  Then use the $EDITOR environment variable in a system call to make the user edit the temp file, and read the results when the process finishes.
This lets users configure which editor they want to use in a pseudo-standard fashion.
How to interact through vim?