Player compulsion is one of those tricky things that you have to really have a good and trusting group and DM/GM to handle and make super rewarding and compelling, and I'm glad this is both addressed and advised on in this Spark, more published material needs to touch on it without simply brushing past it or conversely try and avoid it as something that should never be done! The rival/doppelgänger party is also something that I really don't see come up as often as I think it should given a living world surely doesn't have just ONE active group of heroes in it, so I'm glad that's a large part of this too!
I would maybe suggest defining the Janustone towards the beginning of the Spark, as it crops up a number of times as if the DM/GM should know what it is before it is explained at the end of the Scenes section, which can definitely confuse and put off a less experienced DM/GM.