This is the interesting bit about federation and instances, especially the opportunity afforded by local instances.
You tend to find a World News community on a big, general instance would be dominated by American news sources. A UK based World News would tend to be use British sources and, although we share the same language with the Americans (kinda) we are different (increasingly less these days but things the Americans often take for granted, like guns). The shared language does tend to smooth over the differences - no-one would think a World News community on a Russian or Chinese instance (to give an extreme example) would be the same as a more general one.
So this kind of thing helps us separate ourselves from Reddit and if the Feddiverse is to survive, it can't just be a clone of the other place. I started [email protected], which doesn't have a direct counterpart on Reddit. I'm sure there are many examples of things we can do here a bit differently. If anyone wants something but doesn't feel up to starting it (you should though if you can think of it), then there's: [email protected].
Long story short - I say go for it. You'll likely need a few moderators to keep an eye on things as Feddit.uk grows but the key thing now is to spot a gap and go and fill it.