Interledger abstracts away the underlying settlement mechanism (the blockchain in this case) with a very simple interface. It assumes the underlying settlement mechanism has the ability to send/receive value denominated in a single asset, and that’s it.
This has benefits and drawbacks. The benefit is that it can operate with an extremely diverse selection of systems including any cryptocurrency, any fiat currency, or it can even forgo settlement altogether if two parties choose to do so.
The downside is that Interledger will never have a deep understanding of the underlying settlement network. So interacting with on-chain smart contracts in a generic way is out of scope.
That said there’s nothing actually preventing you from building a service that works like what you’re describing, it just wouldn’t work at the Interledger layer. But you could run a service that accepts paid API calls using Interledger and will submit transactions for people or run smart contracts for people.