Even though Google greatly improved the photo editor in the Gallery app on the Nexus 5, it seems that going forward, that app is going to be replaced with Google+ Photos. This comes from both Google's mission to get users to use Google+ more, but also from the many requests of Android users asking for the "unification" of Android's apps, and standardization of Android. In some cases, especially where Google has its own proprietary apps, that means Google will get rid of the open source app, and continue developing its own. Both the new Sony Z Ultra and LG G Pad 8.3 Google Play devices come without the default "Gallery" app we've come to love.
Many users have also asked for Google to provide a unified cloud storage, like Apple's iCloud, but again that means putting everything in Google's cloud, whether you're a Samsung phone owner, an HTC phone owner or a Motorola phone owner. This move to replace the Gallery app with Google's Photos app is part of that plan, which of course Google likes because it means it can get more users to use its services by default, which again, is something Apple and Microsoft are already doing.
There are some drawbacks to this, especially if they continue to tie their own apps and services deeper and deeper into the operating system, because it means it's going to get harder and harder to fork Android, or to use custom ROMs (which theoretically can't use Google's apps without permission), unless those developers spend more time developing their own open source versions to Google's proprietary apps and services.
I think it's important to recognize that it's very hard to "unify" or "standardize" things when every OEM can pull in whatever direction they want. I don't think Google can take control (at least as far as the user experience goes) of all Android devices on the market anymore, but they can try to control a subset of it, and then hope to expand that subset's market share as much as possible. That subset includes the Nexus devices, the Play Edition devices, and to a degree, Motorola's devices. The more popular these devices will get, the more "standardized" Android will become, under the leadership of Google.
So if you are someone who has always been asking for Google to update (all) Android devices, or who kept asking for stock Android on your phone, and who wants fast upgrades, then you should support this type of devices with your wallet, because right now it's our best shot of ever having a "unified" Android experience that works across multiple devices.