I was wondering this too. I haven't heard anything, and I'm guessing it might be a while before it happens -- if it does at all. If they are planning to do so, it makes sense for them to wait a while after the S5 launch, otherwise features they're promoting on the S5 are available for the S4, and therefore less motiviation for customers to upgrade to a new phone.
I'm guessing it will be a few months if it does happen. I wouldn't hold my breath though.