NovelAI is already a hosted service you pay for. It is specifically used for fiction writing, though it's got a ridiculous amount of neat experimental features, from prefix tuning (a lightweight ad-hoc fine-tuning method which can make the AI write in a specific style based on a training dataset, you can train your own with a custom service they run too or just import one of the thousands other users already made) to keyword replacement for "memory" past the general context limit, to inline annotations ("author's note") which can steer the AI towards a particular direction, style, or theme.
That said if you just want to see how GPT-J-6B works there's a browser demo here: https://6b.eleuther.ai/
