[RyLuke]

The demos and engine are free to use and modify for non-commercial use right now. The repo is here: https://github.com/lynaghk/subform-layout

The happy path issue is definitely one of the big pain points in the "designer throws mockups over the wall" workflow. Simulation of the production medium in the visual design tool can help a bit, but the real solution is to get designers working in the production medium. That's easier said than done, of course. (And ultimately more of an organizational/practice issue than a tooling one.)