I guess I mean that the image could also be cropped by the same node. A keystone distorts the image so that it looks correct on a sloping wall for example. A crop actually cuts parts of the image out. At the moment I don't think there's any node that can cut a triangular piece from the edge of an image, I think that's what I was getting at by crop diagonal lines.
Just another thought - A resolume scene can hold a hundred clips or more, so it seems unlikely you would need to change scenes during your show. As long as the scene is "warmed up" by previewing every clip (which can be done column by column ~30seconds total) the trigger lag will never become an issue.
Magnesson - thanks for the composition - my first attempt at "hard" feedback is here: https://vuo.org/node/2601 - subsequent to that I have made others which are probably better. I think you have the image routed into the FOREGROUND of the blend image node - therefore unsuitable for some applications - ie feedback on the alpha channel behind an image.
What I would love is a simple 2d transform image node! Scaling the feedback doesn't seem possible with "resize image" so to acomplish this I did the feedback with layers.