Some late news: back in April Gwilym Tossell cleaned up an old project line on a roof near Mur Gwyn at Gallt yr Ogof, Dyffryn Ogwen. This is mentioned on page 352 of the NWB 3.1 guide. Restless Roof (7A+) tackles the central weakness.
''I started on an obvious slopey edge in the middle of the roof. From there it is big moves on decent holds until you are over the lip.'', said Gwil, before adding: ''Itís a bit chossy but pretty good.''
The difficulties are certainly not over once the lip is gained, as you can see in the film below that Jack Pearce made. It also includes some interesting musings on the eternal conundrum of bouldering grades (note that the full film title says 7B).