“any feature that makes this easier is a strong candidate to be built early so for inputs just look for features that add ways to connect and make connection easier to the things that come before and for outputs add new formats that follow-up tasks expect or can deal with more easily”

Prioritize features that improve workflow inputs and outputs over standalone ones

Your tool lives inside a chain of other tools — what comes before, what comes after. Features that improve the join between your tool and the upstream/downstream steps compound the most. Import filters and integrations for inputs; new export formats (SRT subtitles, CSV, API webhooks) and enrichments for outputs. Standalone bells-and-whistles that don't touch the workflow boundary almost always underperform integrations.