If Generation 6 will rearrange the type compatibility, I would love to see Grass and Ice getting more favourable changes, since they have some problems that prevent them from being up to par with other types. Also, I read that the developers would consider a new type if they can manage to find balance to it, which would be nice, because that way, we have more room for new type combinations. I imagine that if Ghost didn't exist, then no one would fathom Ghost-types now. Actually, I predict that if almost all type combinations are explored, then there may be a chance a new type may be introduced.
However, first things first: explore more type combinations that's not been explored yet, like Grass/Ghost, Grass/Dragon and Ice/Fighting.
Thanks for reading.