Yeah, I guess I was misleading. There are ways to tie slayers to weaponmasters but no way to make a hybrid slayer yet. Not quite sure why they skipped over that.
They did only do some classes from Forgotten Kingdoms. There is no hybrid hexblade (although you can sort of make one with the feat support), there is no hybrid hunter (again, you can sort of make it with the feat support), not much in the way of hybrid scout. While feat intensive, it's possible to get a domain and/or school into a cleric or wizard hybrid. (In some cases, they may end up updating existing hyrbids instead, so that, for example, you can pick up a school or domain class features via hybrid talent. The MBA classes would be problematic, but a possible solution is:
Give the hybrid classes with MBA based builds an at-will attack power that is basically just a MBA, 'counts' as a MBA, and happens to have the classes name on it, voila. Not the most elegant solution, but avoids problems like double dipping and getting the best of both worlds for striker damage, for example. [Don't give the at-wills power to avoid weird interactions with half-elves, humans, etc].
They still have to do something for Essential classes that don't have dailies ... as you have to give them some choice between taking a daily at this level, or something else from the 'other' class. The assassin poison subs for a daily easily ... they are practically the same thing, but a slayer, theif, etc don't have dailies ... so you have to figure out how to work that out.