Who could credibly replace ITN?
Well Sky are the obvious favourite, being the only other major UK news broadcaster (unless the BBC would be in the running which I doubt)
I reckon if it happens Al Jazeera will give it a go. Definitely a credible provider as they're very well resourced both globally and in the UK, and their plans for a UK orientated channel disappeared so do have some overlap capacity to do it.
The news agencies such as Reuters would be 'credible' but have little in the way of production resources to make a programme.
I'm sure there's a few independent production companies that could do it though they'd need to buy in footage, there's a danger they'd just be turning round agency copy
Would C4's "publisher broadcaster" model prevent it from producing its own news?