Isn't this much more than changing the way ‘display-buffer’ behaves?
IIUC, you want the buffer to pop up whenever some output arrives, the
user should be allowed to delete the window, and when new output arrives
the buffer should pop up again. Correct?
But I'm still confused by how you
want to add something to ‘display-buffer-alist’ and at the same time to
not change the behavior of ‘display-buffer’ ;-)