Murazor confirmed the plans to change the branch of the T-150>KV-3>KV-4>ST-1>IS-4 tanks. IS-4 will move to the 9th tier. The changes will be in the whole branch and the developers think about the introduction of the ST-II tank, pictured below (multiple variants are considered apparently). That’s all we know for now.

https://pp.userapi.com/c837526/v837526727/2f534/TNKl04NP3uc.jpg