The NEC show this year will be Warners led so a new show but in the old Warley slot, I would imagine Manchester is not a threat to a dedicated O gauge show. The killer for me would be the location, it is planned to use the sports centre like the old Wigan multiscale show, that can have parking issues especially if there is a home sporting fixture the same weekend and it's a trek from the station. The location may be more an issue than other neighbouring shows.
But the show space at Wigan is good and they are using two halls, you'll get a lot of O gauge into that space.