That “expense” being only “spending time discussing future topics now instead of starting on the MVP”?
I doubt I need this discussed in any detail. All I can do, now, is hope that this might be a satisfactory solution if that time comes. Because as I said I’m worried (even doubtful) about your choosing a relational database as a back-end – even though relational is the SE way, I fear it’s a baked-in limitation which precludes/inhibits evolution of some features.
I hope so. When a site has even only thousands of extant topics and new people continue to ask novice or “frequently asked” questions, their questions are difficult to receive well.