Originally, the validator set size in the Cosmos Hub was capped at 100, ordered by total delegated Atoms.
The Cosmos whitepaper stated that the validator set size should increase 13% per year until it hits 300 validators as a cap.
In July 2019, proposal #10 suggested a new way to set the validator set size: through governance. This proposal also extended the active validator set size to 125, which still is the current network parameter.
Almost two years have been passed since this last set validator increase and the network has proven its reliability and stability. This proposal suggests increasing the validator set to 150 to improve network decentralization.
Other Cosmos-based networks, like Terra, have already raised the cap to 130 validators, proving that this parameter upgrade is feasible.