Much asked question on here and the answer is nobody knows.
From trade information all we know is that Virgin have shown an interest in the Three / O2 merger talks and were at a meeting with the EU regulator a couple of weeks ago. The EU and OFCOM are against the deal but at suggestion is that some spectrum is laid aside for an MVNO like Virgin to use. It seems Virgin's owners are very interested.
I suspect nothing will happen until a decision is made or the present arrangements run out. EE are now BT and as such a direct competitor to Virgin.