Ethereum

How do people feel about onchain contracts including an optional fee that can be bolted on by frontends? Primarily to incentivize more third-party frontends to be developed.

Are there better ways to do this?

A doodler and computerer. I like permissive/permissionless open source, smart contracts, p2p systems, room-scale VR, and NixOS.

Currently: WhatsABI

I'm interested in this too. Is there an implementation of this I could reference?

Depin Dev hosting /m3ter-heads & building M3tering protocol on Gnosis.
Spread the word; P2P energy is now as real as P2P money
https://m3tering.whynotswitch.com

Swaprouters often have this, e.g. wallets like MetaMask take a hefty frontend fee.