Are there any current Open Access routes that don't go to London?
No, although they have been proposed in the past (the GNWR proposals at one stage included a Liverpool-Hull service I think?).
The two busiest unconnected stations outside of London are currently Birmingham - Brighton: indeed, Brighton's lack of long-distance services but status as 6th busiest station outside of London means that since the withdrawal of this route, Brighton - Birmingham - Manchester is an obvious route from the point of view of possible demand, though don't know about capacity (and of course, it does pass through Western London).