I really like this system at core but there is a thing that occurred to me:
While magic is always perilous, using the same dice size for all boons and banes makes it a bit too arbitrary.
I would add or replace with this:
The player adds d8s to the pool while the facilitator/GM adds d4s to the pool. Keep the same targets: 1-2 trouble, 4+ effect. There is still a level of peril in the randomness of dice but now there is also a certain balance to the caster will and the magic’s danger.