Well, I mean, take Fallout, for example, that'd be semi-far into the future after an applicable apocalyptic event, I guess. If we mean far, it'd probably mean a few hundred years more than that.
actually, we could do a massively fat into the future where some weird shit happened and its fantasy. So we could mix and match. Like, you know the zone in stalker? Like that happened everywhere at once. After a long enough time.....
This actually sounds pretty cool.
Anomalies and artifacts creating new races, old ones being twisted into new forms, a long ass time happens, guns are ancient and ununderstandable devices (mabye preserved so long by anomalies?), and a sort of weird middle ages is happening in the shadows of the ancients.