to that end, why isn't there an option for hybrid pcs
Because as established earlier in the thread there isn't significant visual results to cross-breeding. The individual primarily appears as a member of their mother-side species, possibly with a few
minor inherited traits like odd eye or skin tone for their race. (See Karliah - purple eyed dunmer. Grey prince - Orc with grey-white skin), most these effects can be achieved in the normal character creation screen by messing with sliders.
...on that basis; maybe the dragonborn somewhere down the line actually HAS a dragon in their lineage? - afterall, if the mother was a humanoid.
Best not dwell on the http://www.funnyjunk.com/youtube/2862634/Where+Dragon+Born+s+Come+from/ (NSFW)