I just spoke with someone who received a revise and resubmit verdict on a paper that he submitted to an academic journal. As we all know, there are subtle degrees of the r&r decision, ranging from the enthusiastic (borderline conditional acceptance) to the lukewarm ("we like the topic more than the paper, so if you resubmit, we'll send it out, but we don't really care that much either way").
Anyway, this person received what I read as an almost enthusiastic r&r. In the note the editor outlines what she takes to be criticisms most worth addressing, but does not give the further indications of enthusiasm (such as a promise of an especially expedient review for the resubmission).
The author asked me whether it was kosher to respond positively to the journal editor, indicating an intention to revise and resubmit, but then submit the original version of the paper to another journal, with the intent to publish the original version at the second journal if it is accepted in its current form, and revise and resubmit to the first journal if it is rejected at the second.
My view is that in the case of a straightforwardly enthusiastic r&r, submission of the current paper to another journal is not cool. But things are murky with lesser degrees of r&r enthusiasm. Any views?