What types do you really want to see for the next game? Frankly, there are just some types that I'm surprised haven't been done yet when looking at how many of the same types we get over and over again (Fire / Fighting, Dragon / Ground, etc.). Also, be sure to comment on how you'd like those types to be implemented (what kind of Pokémon, or maybe possible stats or abilities).
Electric / Fighting
Normal / Ghost
Fairy / Ground
Bug / Psychic
Bug / Dark
Rock / Ghost
Really want to see Normal / Ghost. Maybe some sort of Dunsparce evolution named "Dunspecter"
Inside there was a bread roll! ...But it bread rolled away
They reuse old type combinations because they have designs that fit those types, and if all the dual types were released at once, there would be NO MORE POKEMON. No more, at all, for they would be COMPLETE.
Instead of complaing about types that haven't been used yet, it might be a bit more constructive and friendly to the perpetual existence of Pokémon yo discuss type combinations that already exist but for which new representatives are necessary, like Steel/Flying, Ice/Flying, Electric/Ice, Electric/Grass, Electric/Fire, Ghost/Fire.