I don't know if it would be busted, but I would love for them to just follow how it works with Cities. Your general determines your special battleline (beyond clanrats and stormvermins) and then just pick the clan as a subfaction. So Skryre generals gives Stormfiends/Acolytes, Esshin Gutter Runners, etc. I guess the main problem with this approach is that it's probably not thematically accurate.