So, I've found my Imperial Guard Collector's Edition book, and saw this guy:
And after some thinking, I decided to make some rules for it! Because there is only one better thing than a Leman Russ: a Leman Russ on steroids

!
KING RUSS 175 POINTS
The King Russ is a single Elites selection for an Imperial Guard army.
King Russ
BS 3 |
FA 14 |
SA 13 |RA 11 |
HP 4
Composition:
• 1 King Russ
Unit Type:
• Vehicle (Tank, Heavy)
Wargear:
• Turret mounted battle cannon
• Hull mounted heavy bolter
• Searchlight
• Smoke launchers
Special Rules:
• Lumbering Behemoth
OPTIONS:
• May exchange its battle cannon for:
- Vanquisher battle cannon free
• May exchange its heavy bolter for:
- Heavy flamer free
- Lascannon 15 points
• May take a pair of sponsons armed with:
- Heavy bolters or heavy flamers 20 points
- Multi-meltas 30 points
- Plasma cannons or lascannons 40 points
• May take any of the following:
- Pintle-mounted storm bolter or heavy stubber 10 points
- Hunter-killer missile 10 points
- Dozer blade 10 points
- Extra armour 15 points
- Camo netting 20 points
• May be upgraded with one of the following:
- Command Tank (friendly units within 12” may re-roll failed Morale, Pinning and Order tests) 15 points
- Tank Ace (gives BS4 and Tank Hunters) 15 points
- Mechanicus Crew (gives It Will Not Die and Interceptor) 15 points
So this is in fact a beefier Leman Russ in the Elites slot and with corresponding special upgrades. The Mechanicus Crew is funny: please note that Interceptor works against everything that comes from reserve, not only against Flyers
.