Thank you for your future consideration,
Thanks for the question.
Unfortunately based on how Yellowfin is designed (reports are based on views and views are based on data source data) this functionality is highly unlikely to be implemented in the future. This is because it would require a complete redesign of Yellowfin's underlying architecture (each report and it's definitions are connected to specific views).
I know this likely isn't desirable for you, but the best solution I can offer would be to create a co display report consisting of one table built from your prod view/data source and another table built from your dev view/data source. You could then display this data side by side.
You could also consider taking advantage of Advanced Sub Queries -- which allow you to query data from separate data sources or views and then display the data in a single table.
Anyway, I know this information isn't exactly what you were hoping for, but hopefully some of these alternatives can work for you. Please let me know if you have any questions or concerns.