Any expansion of terminal space at EDI will most likely be filled with retail outlets. The shambles that is Edinburgh is no more than a shopping centre with a runway, where passengers are an afterthought till they reach the shops.
I used to pass through the airport 3 or 4 times a week, thank heaven I don't have to do it anymore, twice a year on holiday is more than enough.
Wait and see, I think you will be pleasantly surprised.
There will definitely be a new permanent immigration space and additional gates with gate rooms which are linked directly to immigration. The extension should also allow an expanded check-in and baggage areas.