In our client, we decided to migrate to Cosmos React when it is ready for CSHC. The projection is that it will be ready late 2021 or early 2022. Meanwhile, we're developing for Cosmos React ready everyday today so that the migration in future will go smooth. Using design template for sections, data page, OOTB controls, etc. and avoid custom coding are important (for complete guide - https://design.pega.com/getting-started-design-system).