First, custom keyboards: Some users outside English speaking countries sometimes find it hard to accustom to Apple input methods such as Chinese users. So it is been considered by Apple in iOS 8. Third-party developers can use their self-developed input methods.

As to photo edit and share functions, you can search on the Apple website to find what you need.

Moreover, every Apple device user can download iOS 8 to try it. But just as it is the biggest iOS release ever, it needs your device have enough space to update. This means if your device is 16G or smaller, you have to delete some apps.