Thanks a lot to our Russian insider.

https://thearmoredpatrol.files.wordpress.com/2016/01/chieftain_mk6_2.jpg

„WG is planning a Chieftain tech tree branch. They also plan other lines too, but let’s talk about this one for now. The Chieftain line will likely split from the Valentine, with most probable tanks to be in it being the A38 Valiant, AT-1, and the Heavy Valiant. The Chieftain will top it off as the tier 10. They were planning it since the last year’s summer or even earlier, I don’t recall that far. The line is still a prototype so it can always change its structure. In the last few months, WG changed the classification of the Chieftain from Heavy to Medium a couple of times, but right now, the Chieftain is a Heavy. The line is somewhat urgent – ETA late 2017/early 2018. A Brit scout line is also in the works.”