I'm not sure a mechanism that relies on making BTC transactions is great because the UX would be very bad (and near unusable for normies). 

I feel like there are probably some other heuristics you could apply to npubs (looking at follows is just one) to determine their credibility without requiring any user action. Stuff like "age of oldest event" or "count of times blocked by credible npubs" could do a lot. 

 Ecash is much simpler than you imagine 

 If it's ecash and not on chain then yeah I agree that's a much lower barrier to entry