Yes, we should certainly provide easy ways for those holders to become validators.
a) Indeed, something like Rocket poot or Diva (a newer liquid staking protocol, also focused on decentralization)
b) making Dappnode even easier. Right now you have to buy physical hardware. A compromise could be a cloud solution that can be set up in minutes. This would be less decentralized than your own physical hardware but still more then using liquid staking
Those 2 addresses are Stakewise and Kleros. I think for those 2 we should not aim to reduce their absolute numbers - but instead increase the total amount staked so that their relative number goes down. E.g. Kleros holds 19.2k GNO out of in total ~3m - that is merely 0.64%.
The easiest way to do this (without touching the protocol) is to add transaction fees/ MEV (at least after the merge). We could e.g. simply write a contract that can only be called by the “miner” address (the creator of the block). This could even exclude the addresses of the largest known stakers if desired. Such a change would be much easier to do than actually changing rewards on protocol level which would require a hard fork and this always a lot of extra effort for protocol teams.