"a nice fall-back would be the ability to have more than one image in a step. There are many valid reasons for wanting this, one example being a before and after shot. That’s not two steps, it’s one step – do this and you should get this."

I've just tried the demo version of Screen Steps and as far as I can see you can have two images in one step.
Don't enter a step heading in the text bar above the the second image.
Then when you export this, say to PDF, both images appear in the same step.