If you use a sub namespace I would name it differently. So that it also fits other variantes, that are not default but implemented by others.

e.g. DisplayActionEventFunctions or so.

Minor issue/nice to have:
I think, I would change the function name to express more what the action does. "default" is very subjective and not always very helpfull when reading the code.

Additionally I think the default should some thing else in the future and more locally than the old implementations.

Maybe? e.g.
DefaultMoveAction -> MoveSenderCameraAction
DefaultSetCrosshair -> SetAllNonSenderCrosshairAction