To be honest, if you can't produce a basic, high-level feature roadmap within a day, something is SERIOUSLY WRONG with your development as such a roadmap can be easily based upon internal development goals.
I was looking at the game Blightbound yesterday, which had just released on Steam's Early Access, and their website has a list of upcoming features. They split it up based upon Early Access release, two follow-up releases, and other future features. In each release, they list the planned features for that release. That showed me that the team has an idea of what they have prioritized as important features and when they're planning to implement them. The only unknown to me is whether the team is truly capable of completing it. (They should devote a decent amount of time to bug fixing after going into a sort of public beta phase like Early Access.)