i dont think that they'll use second types that they already used for some starters (flying/gorund/fighting/poison)
they are goin to make hikozaru pure fire cause 1 is missing(;154;;254;;157;;160;;009
types that the starters could have as 2nd:
psychic,steel,rock,dark,ice
types they wont have:
ghost(nuh<.<),dragon(resist.to any starter),normal(they would give it to cyndaquil if they wanted to),bug(the grass starter is always reptile/dinosaur thingy),electric(doesnt sound good as starter type)
psy: could be used for any starter
dark:same
steel:works with fire/grass
rock: only works with water
ice:works with fire/grass
so when i look at the D/P starters i'd say that naetoru will have steel as 2nd
hikozaru pure fire (i they're planing to make the 2nd pure in the 5th gen then he's going to be psychic)
pochama psychic or dark
but thats just my theory =o