So United will be able to unite all its operations, but VS / DL will be split between terminals 2 & 4.
VS remain in T3 with domestic launching from T1 and moving to T2 which was designed with a domestic in mind for bmi. The DL / VS thing is recent thing and although DL might want to move their operations to T3 it might take some doing as it's 8+ B767-400ERs rotations needing gate space. Added to the fact that the rest of Skyteam partners and the Skyteam lounge are in T4 which was remodelled for Skyteam and is hardly bursting at the seams, it would make operational sense to move VS to T3 as they are currently in what will be the Oneworld Terminal. Sticking point is the Virgin Clubhouse.
VS actually use gates that were used by BOAC B747-100s on delivery and haven't changed much since.