There is no way they will move one of GLA's two daily flights - these are well utilised. A daily flight to EDI in place of a third flight to GLA could operate at any time and wouldnt be restricted to morning or evening.
Nobody is saying that EDI is the be all and end all however it serves Scotland's capital city, has huge inbound growth potential and is by a fair distance the busiest airport in the country (and please - that is not to belittle the success of GLA in any way, shape or form). Its therefore not hard to see why the might want to add Edinburgh to their considerable route network.
EDI are currently working on reinstating a widebody stand capable of handling a 77W - and boy do they need all of the stands they can get at the moment.