Pokemon GO developer Niantic announced that it'd soon be stopping support for devices not capable of running iOS 11, and it's a bit of an odd one to feel out.
In Niantic's most recent it's explained that older devices, such as iPhone 5 and 5c or fourth-generation iPads, will no longer be able to play Pokemon GO since they can't upgrade to iOS 11.
This is down to the fact that older devices simply don't have the operating systems to handle such a load. As it says, "This change is a result of improvements to Pokémon GO that push the application beyond the capabilities of the operating systems on such devices."
While this may not be much of an issue to a lot of users out there, it's a bit of a tricky one overall. On one hand Niantic just wants to keep improving Pokemon GO's features and give players the best experience possible, and that comes with higher and higher strains on the OS.