I was considering the idea of allowing a generic Heroic Exertion action which can be used in several ways on any skill use you are trained in... make it reliable, break the limits of effect and so on.
The hardest part of that is how does one generalize the idea of "extending beyond the normal limits achievable by skill in an activity "..... Perhaps practices define those explicitly
OK, so going on with my concept of "Checks always regulate conflict, and conflict is always handled by a challenge", then a ritual/practice is a check, meaning it helps resolve conflict, and thus it is always part of a challenge. Now, you can always do SOMETHING in a challenge to move forward to the next check (presumably, if not then the PCs are stonewalled or defeated, we will assume this doesn't happen in any reasonable D&D game).
So, what is the actual role of a ritual/practice? It has to be to provide a different option to the character. I mean, you have some fiction, and the player is going to describe how the character utilizes some resource he's got, skill, power, ritual, etc. to move the fiction in his desired direction to achieve a success. So, skill training simply adds to your success rate when you can engage the fiction in a manner that invokes that skill. Knowing a ritual would likewise simply add a resource that allows specific narrative options. The characters are in an SC to see if they can arrive at the Temple of Fate before the Wicked Witch. Casting
Phantom Steeds is pretty clearly going to help achieve that, so the Wizard does so, and the party sails over the Forest of Grim on misty flying horses, 1 success!
Honestly, given that the ritual/practice has a cost, its not clear to me that it shouldn't be an auto-success. Maybe it should become an easy check. I'd give an auto-success for burning a daily for instance. Anyway, then my point about page 42 makes sense too. You can create an 'ad hoc' ritual/practice in essence and maybe it helps you, but it has a cost for sure, and the benefit is more problematic. Maybe such things are always hard checks.