I'd imagine that the Pred/Jason sales were better than the actual MK characters. I have no numbers to back that up but it's more likely to be this way. Mainstream loves guests... they don't even know who is Bo and yet he managed to make the cut.

WB must have an influence in this, they want sales.. they want $$, if NRS ( despite all the fuck ups they did in their games) were that bad, they would have turned the whole pack into a guest pack and the everybody will but it but you.

The best you can do in my opinion is to buy the Bo and Cyborg, make sure that you don't contribute to the sales of the other guests if you don't want em.

Even if they had KP3 (highly doubt it ) expect even more guests and trim your wishlists.