How relevant is "moving on" as an argument in peer review?
The way I see it is as follows: the reviewer's primary job is to judge whether the main claims made in the paper are borne out by the evaluation. The editor's primary job is to fill the conference/ journal with the papers that had the most interesting claims and passed review.

If you send in a paper, and the reviewer complains that additional research is needed, you actually have two options: you can add the research, or you can reduce the strength of your claim. If the editor complains that the claims are not interesting enough, you should look for a less prestigious venue.

So in short, it's perfectly fine to publish unfinished or negative research, but you need to be very honest about it.