We do not know Apple's plans and are not allowed to speculate. But the with way iCloud Photos is working, it would not make much sense with a larger iCloud storage plan. iCloud Photos is not an off-site storage to use as an external storage. nd you cannot share your iCloud Photo Library with your family, only your storage plan. iCloud is a syncing service for a single user, to keep all your photo libraries on all your devices identical and in sync. The available storage on your smallest device will limit what you can keep in iCloud Photos. even if you are using "Optimize Storage" on a device and do not mirror all photos on your device, you will need at least enough storage to keep the optimized versions for browsing, as a rough estimate 10% of the size of the library in iCloud. So, if your iPhone or iPad have 256GB of internal storage, you could keep a 2TB iCloud Photos Library in iCloud, without clogging up the iPhone or iPad, but more would not be possible.
If you want an off-site storage for a large photo library and the ability to share it with family members, iCloud Photos would be the wrong choice for you. It is perfect for keeping the libraries in sync, but there are better off-site storage solutions.