I don't think that layouting big workflows is so big issue, because big workflows are hard also for users and should probably be splitted to multiple smaller ones (e.g. using parallel workflows or changing workflow by moving content to a folder with a different local workflow).
@datakurre don't forget the huge workflow I showed you in Bristol... Whether we allow users to create big workflows or require them to break it up into multiple workflows (then have to add the 'move to different folder' logic, or add UI for parallel workflows) still ends up with the same overall complexity. We also had seen that once you give power users a tool, they will find ways to exploit it in ways you wouldn't have imagined!