serious note: possibly not. the UK too small to be it's own game wouldn't make sense considering previous regions have been based on areas considerably smaller than the UK itself, (regions of Japan, New York) France being the only bigger one (If that, don't know how they match up in size). It's interesting enough imo to be own region if they ever wanted to.
The post-E4 Area might be in the region itself, Unova did this, to some extent Hoenn too. Or the Channel Islands, Jersey and so. Which aren't part of the UK, they have the same head of state but aren't part of the UK.