I’ve been noticing a certain trend in common spoken English: people have no idea what they’re doing with case. For instance, the accusative case is now being used whenever it comes after the verb, instead of only when it’s an object of some verb; eg. “I’m not as good as him.” While I would postulate that the language itself is changing in this direction, I hear things like: “My father gave those to my sister and I” and “Whomever can hold their breath the longest wins.”1
It’s the classic “deterioration of language” phenomenon, which usually isn’t deterioration at all. I just don’t see where this particular change is simplifying things. Case might be working its way out of pronouns just as it has out of nouns, so we’d get a very order-dependent language (yay, making things even more ambiguous for us computational linguists).
1But all is lost with “who” and “whom” anyway, since very few people, even in the educated world, know what’s going on there.