Text size
Text size is an extremely common accessibility complaint. Control over text size is common on other platforms, and is now starting to be seen to a limited extent on consoles.
However default text size also needs addressing, ideally adhering to a minimum of 32px @ 1080p (46px for text that appears for a limited time, such as subtitles/captions), particularly if text size is not configurable. Although it is rare, some games (such as Warlock of Firetop Mountain) do offer control over text size, so a system level text size preference could be a good candidate for exposing to game developers.
Configurable text size in iOS, reflected in the system UI and apps that support it
Next: System font choice