After looking at this British heavy tank project, I could only call it a Super Churchill. However, since a Black Prince got the Super Churchill name first, and this tank is even more super, the only name it is worthy of is Mega Churchill (aside from Super-Duper Churchill, to show off how silly it is).
The most interesting thing about this tank is the quad engine location. Even if your engine does get knocked out, you only lose a quarter of your engine power, and only an eighth once your crew repairs it. This is good, since at a mere 8.7 hp/ton (about the same as an elited Churchill I), this thing isn't going anywhere very quickly, especially at the projected 32 kph.
This tank appears to be a better Churchill I, and, since the British already have a tier 5 premium Churchill, is probably tier 6 material. While neither of those guns is particularly amazing at that tier, preferential matchmaking, and in the future, multi-turretedness, might make this thing worthwhile. Maybe those 20 mm AA guns will even be activated, to spray steel at those pesky lights and mediums that are going to be running circles around you.
However, until multi-turrets are implemented, it can have another role: a British premium TD! Disable that turret, and it's a bigger, (much) fatter, Alecto. With a bit of a boost to the gun, the Mega Churchill Gun Carrier could very well fill a tier 5 TD role.
Edit: apparently the 65 mm did exist. It was called the 8-pounder AT, but wasn't that much better than the 6-pounder, and the project was discontinued. That makes a Gun Carrier role that much more likely, since otherwise it would just be a fatter Churchill III. -EE