Yes, you definitely ought to join the waaagh! then. It would be cool also, if you have it done in time, to get in a game for Agent of Change's campaign, so we can have the rebels included in the batreps.
I haven't used the Grot heavy weapons myself but I've taken a whole lot of tragic rokkit fire from killa kans with a number of my armies, and it is quite frustrating when they hit. Also, it's annoying if you only damage once each turn, as the damage inevitably all goes to one kan, while the others continue on their merry path of destruction.
Zzap guns are basically quite expensive compared to rokkits, which [excluding termies] are generally more killy almost all the time. Zzaps do have better AP, but even then, a single Dred CCW will do far mor damage in one turn than a Zzap is likely to do all game, especially once you factor in cover. Plus, the range on the Kannon is larger, and in the next edition it is rumored that the blast weapons will scatter instead of rolling to hit [as a salvo] and get full hits on all models, even those only partially covered. So, two or three blasts placed as a salvo will be awesome vs enemy horde armies, and they're also useful against tanks, and their quite inexpensive for what they can do. All reasons to consider them. If I had to, off the top of my head I'd go with a heavy support section that looked like so:
Killa Kan, rokkit
Killa Kan, Rokkit
Coupled with your current fast attack that's some pretty good AT power, and adds a lot to combats [where your ridiculous numbers and some powerfist attacks may actually let you pull through, especially if the grots teleport out after a round or two!].
Again, just some thought. I'm more interested in seeing how this plays than in offering suggestions.
I look forward to some batreps once you're done!