There are a number of options for the Hellcannon in a new CD army book:
Keep the Storm of Chaos rules
Easier to field
I’ve written some new rules based on the SoC rules which incorporate the last three changes. I wrote them before the Projects all started so I hope I’m not treading on anyone’s toes here, if you’re interested then you could move it over the that section. It is at about 200pts at the moment to keep it as nasty as a huge honking cannon with teeth should be, and the rules definitely need some balancing (which is really hard to do since keeping it powerful means keeping it unreliable, which means either win-big or lose-big, but while we aren’t O&G we also aren’t Dwarfs) so I’d like a little input on where other people think think it should fit. Less than 150pts? Unlikely to go rampaging? Strong shooting? Reliable shooting? Hydra-style rules? (Bear in mind that you can’t have it all).
I’ll post my current rules if people are interested in that more than anything else. You wouldn’t believe how many rules there are just dealing with basic movement and combat. Saves doing an FAQ though.