I don’t think it will happen until there are enough informed users, unique information and welcoming communities that create a strong reason to come here. Currently it’s quite nice and these things do exist to an extent, but due to the relatively small size the communities feel much less bustling than those on Reddit and I don’t think most people we see any advantages to use Lemmy over Reddit. Lemmy will gradually grow, but unless Reddit completely implodes I doubt there will be a significant enough migration here that we would be able to call it mainstream.