Wallbreakers damage bonus v golems
Not that I really think that any of this would be implemented (or used if they were), but here's a little fun for wb:
A wb placed in a defensive clan castle could have a favourite target of a golem, and get the defensive bonus.
Basically, wall breakers are useless in the cc on defence. They run up to things and blow up doing (without the damage bonus) nearly no damage to not much at all. Golems on the other hand are basically walking walls with mega health that meander through a base more or less unstoppably immune to most traps and damage dealing defence (until of course they run into a wall they'd like to open while the support walks around).
Would I want wallbreakers in my cc even with the bonus? Probably not. It might be a fun surprise in a war cc. I can't see it rebalancing attack massively in favour of defenders, and would be an entertaining way of thwarting a gowiwi or gowipe once every other blue moon.