Apple will no longer update or maintain Aperture. That means features and functionality will slowly begin to break as OS X and the hardware platform is updated. Aperture will not suddenly stop working in the near term. I continue to use Aperture for all of my processing.
Apple Photos is the replacement for both iPhoto and Aperture. The general public doesn't really know what it will be capable of or not. There is an assumption that Apple will not abandon the basic image engine of Aperture. That would make sense for migration. Nobody wants to lose the adjustments they made to images. I got the impression that Apple will not be designing or implementing advanced image manipulation features into Photos. They will rely on plug-ins. I see this as a trend Apple is following with trying to monetize customization and advanced features for all of their products. Take a look at what Apple did with custom keyboards with iOS 8. You can finally have Swype but it will cost you $1-$2. Same thing with ringtones way back. Remember how some people went ga-ga and bought ringtones for $0.99? Going back to Photos you can imagine buying plug-ins from the App store for features like noise reduction, custom dodging/burning brush shapes, etc. The burden on Apple is now much lower since the development has now shifted to 3rd parties. All Apple needs to do is maintain the framework and some basic features.
Anyways, that's just my guess.
Personally, I have been very happy with Aperture. Whether on accident or on purpose, I believe Apple designed a very nice workflow structure - for me.