Ceramic node to use Helia rather than separate IPFS?

No, we have no plans to use Helia at the moment. We’re actually currently working on moving away from Kubo and moving towards a Rust implementation of Ceramic that will utilize the rust implementation of libp2p directly for the things we currently rely on ipfs/kubo for, and will also replace some of the ipfs/libp2p protocols we currently rely on (such as gossipsub) with our own custom libp2p protocols that will be more efficient and scalable for the needs of Ceramic. See CIP-124: Recon (tip synchronization protocol) for more information about our new data synchronization protocol we are in the process of building.

In the long term, as the protocol stabilizes and matures, I could imagine someone building a fully javascript-native implementation of Ceramic that uses js-libp2p and re-implements Recon and any other Ceramic-native protocols in javascript. I could also imagine compiling the Ceramic Rust implementation to WASM so it could be used in browser. Neither of those ideas are a priority for the Ceramic core dev team at the moment though.