Loving all the speculation. to offer my 2 pennies....
Marseilles - Great for adding France / city destinations but difficult to justify, due to limited 'beach' offering.
Bulgaria (Burgas/Varna). Heard quite a bit of speculation on this, and would be a good shout. Only issue would be how much they can get. at 4hrs from the UK, could they get the revenue they need to keep it alive? (regardless of which bird they use)
Tunisia - They dipped their toe in 2011 - didnt work, tried again 2015 - terror attack. Sensing a theme of 4 years here so maybe back on for 2019? It is on the up again.
Egypt - Would imagine only the B752's could realistically do it, isn't it right on the limit for B738's. 733's have no chance
Iceland - can see the appeal, but with the large amount of incumbants across the UK, and it's preference for transfers to the USA, i'd be surprised.
GIB - would be good, but the 738 restriction will hold this back, unless it's solely on B733's (B752 in MAN due to no 733's based)
The remaining 3 bases should be on sale in the next couple of weeks so we may find out then...