I think think that to get a healthy diversity of active validators a different level of care is needed for each group.

Harmony could set good guidelines for what a healthy validator looks like based on type.

Exchange: a healthy exchange validator provides 0% rewards (100% commission) the reason for this is because they'll have a large amount of stake coming in, and so by providing any kind of reward to what will be perceived as the top node will direct new users to stake for a validator that already has a sustainable support system.

Communities: You could require web, twitter, and other data, and have a specific day of the week dedicated to these kinds of validators to provide initiatives to what will be your more decentralized groups.

Institutional groups, may need further assistance, so you coudl link them up with Pops and others teams that specialize in coaching new validatiors onboard and provide incentives to those teams for providing support, as well as requiring that institutional groups again.... (provide limited rewards maybe 50% as an example)

General guidelines set forth by the blockchain itself well have a huge impact on how the community sees the blockchain itself and will greatly influence how they participate.