Considering we have gotten Grass/Ghost in 3 generations since its introduction as a type in gen 6... i doubt them running out of type combinations is an issue.
Like... the type combinations we have most off, are either combined with Normal, Flying, Poison, Grass or Ghost.
We have 8 Grass/Ghost types (4 of which are introduced in Gen 6 and 2 in both gen 7 and gen 9).
We have 14 Grass/Poison types (9 of which were introduced in Gen 1)
We have 27 Normal/Flying types
Like whats noticeable in gen 9... is that type combo's that were previously very rare... have been revisited and now we have gotten multiple off.
Take for example Water/Fighting, which has been Poliwrath exclusive before 2 more Pokemon got the type in Paldea
The last Grass/Dark type we got before Zarude... was introduced in gen 3... as such also a rare typing...but in Paldea 3 more got them (Which makes the typing less rare).
Grass/Ground was Torterra exclusive... but then 3 more Pokemon got it in Paldea.
Other types that are still rare are Electric/Grass (While we have gotten 3, technically we have one cuz 2 are Hisui forms which don't exist in modern day), but we also only have 4 Grass/Psychic types... 1 of which is a legendary and one of which is a legendary. But we've also only gotten Grass/Ice once...
So there are a lot of type combinations that are rare and could use more mons off, while other types we can get less combinations off.
