Edinburgh Airport was bought out by an infrastructure company, with the explicit aim of growing the airport and selling it on for a profit. This was clear from the start. For any such plan to work, they need to grow the number of flights for minimum expenditure. This is exactly what they have done.
If they sell it on.. the new owners are going to want to recoup their money as quick as possible, which means further growth and minimal expenditure.
Don't expect the terminal situation to change any time soon. Any owners are only going to be interested in the short term.