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Currently there's no way to do it. There's a request for this to be implemented here.
Affinity applications don't share any code with Serif line of products for Windows. So no, it will not be integrated in Photo.
I've only installed LR5. To get the plugins you need to do the following:
- create a folder where the plugins get installed
- start NIK Collection installer
- when compatible applications are shown click the '+' and add the previous created folder
- do the installation
- add the folder you created and where the plugins are installed to Photo 'Plugin search folders' and '/' (this is mostly 'MacintoshHD')
Restart Photo and you should have the NIK plugins available.
Background information: it seems like the installer of the NIK Collection does not install the plugins which are needed by Affinity Photo when you have LR only on your computer and choose the normal installation. You need to do the steps I described to get the plugins if you don't have Photoshop installed.