I bet those "sources" decided to look at summer 2016 on the EI website and concluded because 5 daily is on sale that's what happening (couldn't be more wrong btw). I can't see a LHR link but been able to book connections ex LGW will be a boost in itself.
Would also say if LHR was the plan IAG would of brought it up during the sale as it would of been a big + for them getting approval from opposition parties.
EI also hold more slots than stated!