I am not sure the Beeb news blog is right. TfL overseeing part of a former franchise is what happened when the Silverlink Metro Operations were separated from County, which is now part of LM.
... but .... routes handed over to London Overground are West Anglia Liverpool Street station to Enfield Town, Chingford and Cheshunt of the 25 stations 23 will transfer to LOROL with Liverpool Street and Chingford stations remaining Greater Anglia/Network Rail run.
http://www.bbc.co.uk/news/uk-england-london-23144343
TfL contracted operations to LOROL, and their contract has been extended to 2015. These will be tendered separately, as they are very different animals. The station that will remain with Anglia is Cheshunt not Chingford. Cheshunt will have more Anglia services stopping, and for the moment Hertford East hasn't been included. Anglia's stock sidings at Chingford will eventually become part of the TfL package. This is probably because Hertford's will become Semi fast, with the TfL locals running to Brimsdown on the new track.
As for stock, I was telling a local meeting on Monday that an FCC rep was misleading Haringey Borough, as GN inners have no replacements planned for their scruffy 313s. They are 3-4 years older than 315s. FCC man agreed with me that they need to discuss 313 refurbs as an option!
So expect a major refurb of 315s for the Enfield / Southbury and Chingford lines. And Stratford - Brimsdown. Remember 378s came on the back of serious overcrowding on the North London, and the Olympic Travel Plan. Refurbished 8-car 315s going back to Jazz Style 10 minute intervals are likely to run for some years yet.