General feedback:
I feel like we should try to move away from MPTs for proofs, because they are so big compared to other proofs. Have you looked into things like Verkle trees to reduce proof sizes?
When sending assets to someone, you need their account details so you can know (for example) how much gas to provide (if the recipient is a contract wallet you’ll need more than 21,000). I wonder if when someone shares their account with you via QR code, we could also fit their account proof in the QR code so the sender can properly construct the transaction without any third party involved?