You can already buy on Freetrade etfs that try ride on the aggregate activity of investors on various stock markets and of various investment theses already: there are a few index trackers to choose from.
If you believe the market looks reasonably efficient to the average retail investor, then it should outperform a smaller segment of investors - Freetrade users. If you believe Freetrade users have an edge on the market, they should outperform VWRL or whatever. (Of course we’ll only clearly see which is better in hindsight, but you know.)