BBC World News should be the last of the foreign services to be sacrificed - the non-English services should be axed firs.t. It's fine for the BBC to provide content in multiple languages when the cash it there - but when it isn't they should be the first to go.
As for this plan - merging the news channel and World News just won't work for either audience, but that's not to say something can't be done. I think though they would effectively need to close them both and relaunch a new leaner, meaner operation which ideally would still allow for significant opt outs at points in the schedule where required.
Yes, both Farsi and Arabic should be axed first.
As for merging the two english news channels, it will only work if NC is replaced entirely by World News with Domestic opts. The editorial integrity of World News must not be contaminated by UK news that is irrelevant to international viewers.
Half of the Weekend bulletins on World News are only short summaries. These could easily be simulcast allowing the same presenter to cover the domestic news as well. Potentially meaning an entire gallery could be vacated for several hours during the day. I'm pretty sure the 2am bulletins are done like this already as recorded programmes air on world from 2:10. (Caveat: not sure if this is all regions.)
If all the current BBC One/Two simulcasts continue, the weekday daytime schedule could be exactly as it is today. (I cant see them simulcasting any of the Studio B 'branded' news programmes or World News America.) However, I'd like to see them drop ALL of the domestic simulcasts. (Breakfast, Derbyshire, 1, 6, & 10) and the pointless Newsnight repeat. Thus giving the UK viewer 6+ additional hours of programming daily.
And for goodness sake dont call this new combined channel 'The BBC News Channel'. The name 'BBC World News' is a bajillion times better.
EDIT: Rolling news needs to die, so i dont agree with ginnyfan's idea. Also, many of the World presenters are of a higher caliber to domestic. I'm also not sure that pairing presenters up would solve any problems.