There are various kinds of features that frontends would want, but not all features are useful for every frontend.
For example, one frontend would want to have an AI chatbot as a feature, while another frontend would not need it.
So perhaps these features could be added as optional plugins to Orbis. In a sense that an Orbis node operator could choose whether to support certain plugins, or not.
So we could have an Orbis node that has an AI chatbot plugin (connected to OpenAI's API). Any frontend that needs this feature would choose to connect to this Orbis node instead of connecting to another one without the chatbot plugin. The Orbis node could also charge frontends for the usage of the AI plugin, which brings revenue to the node operator.
There can be many plugins doing all sorts of things, from accessing certain data (like financial data) to processing things (like sending emails or doing cron jobs). And a whole economy can be spun around them bringing revenue to Orbis node operators (and thus making running nodes sustainable).
Would love to hear your thoughts on this :)