While this would get the effect of more users, it goes against what decentralized services are intended to do. One of the biggest things that decentralization brings is that Lemmy does not become another Reddit situation happening now in 7-8 years, if users are spread out over many instances, if Lemmy decides to pull a Reddit or a Digg, you can just go another instance instead of having to abandon it entirely.
Sadly it's not a problem that can be easily solved by pointing users to a single instance, because then, ironically, you fragment the fragmented community into an "us vs them" situation against the lemmy.ml instance if anything were to happen, with lemmy.ml always winning because that's where the users would be.
I think having a short list of general purpose instances, maybe 5-10 or so, where it chooses one of them at random and lists the others under an "other servers" button is the best compromise to this, as it spreads the load out across trusted instances, while also not leaving a single instance to become so big that they essentially control the entire network.