You'd have to say that the major worry for England at the moment is that beyond the first XI, the others who are likely to make up the World Cup 15/16-man squad don't look likely to make an impact if called upon. At the moment, we're looking at a first XI of:
Tres
Strauss
Vaughan*
KP
Fred
Colly
GoJo
Giles
Plunkett
Harmy
Jonah
With the other five being Prior, Solanki, Blackwell, Anderson, Bell and Tremlett, the forgotten man. I'd like to think that potentially Shah, Cook, and Joyce will all push their claims to replace Solanki with the bat; I'm happy with Prior for now as I think he has potential, likewise Bell is deserving of more chances IMO.
Jury still out on Anderson at the moment. Blackwell showing signs he could be worth another series - some useful bowling and slightly more responsible batting, the unfortunate thing being he hasn't had a chance to show what he's best at from no8.
Kabir is probably not worth persevering with - his batting was good today and he picked up a couple of handy wickets, but he's still unreliable and doesn't give us much we don't already have, hence Tremlett gets the nod if fit. That covers the extra five named there.
As for their potential replacements, I've mentioned three batsmen already who can bat in the top 5 - all of whom I would expect to make their ODI debuts in the next 12 months. Potential replacements for Kabir or Anderson are Tremlett, as already stated, and Simon Jones will come straight back in - Gough doesn't seem likely ever to play for England again, so we're probably still looking for one or two more seamers to press their claim in domestic cricket. Perhaps Sajid Mahmood will make a comeback, or Stuart Broad will do an Anderson and appear from nowhere - who knows.
One thing I can say is God help us if Fred gets injured.