Gasless decentralized transactions with DAG can solve a huge problem of web3 adoption. But smart contracts don't provide the flexibility and control over the design.
According to wiki, https://wiki.iota.org/smart-contracts/overview, multiple blockchain can be anchored to the tangle. Will IOTA provide shared security to substrate blockchains?
Developers will not need to learn a new framework as substrate is already a robust framework and multichain future is met.