Ok, registered dev here with Yosemite and iCloud Drive.
Photostream is legacy - when I just took a photo on my 5s with iCloud drive and photo stream active, the photo appeared in both my iCloud drive on my iPad and on the photo stream in iPhoto.
Eventually photo stream will not exist even on the mac when they release the new photos app.
So don't freak out - hopefully you have access to your photo stream on another iOS device thats not on 8 or on a mac with iPhoto installed.
Photostream is legacy - when I just took a photo on my 5s with iCloud drive and photo stream active, the photo appeared in both my iCloud drive on my iPad and on the photo stream in iPhoto.
Eventually photo stream will not exist even on the mac when they release the new photos app.
So don't freak out - hopefully you have access to your photo stream on another iOS device thats not on 8 or on a mac with iPhoto installed.