On the main bucket & spade routes inbound traffic really is a non-issue. But yes, of course sufficient demand to fill an aircraft is of course required and with no base at INV and ABZ, it's probably unlikely.
Allocated seating. According to a communication a few weeks ago, it is still being considered along with other ways of "making the Easyjet experience better". Very generic but that quote was made in response to questions regarding FR's trial and whilst it's not very specific, it does indicate that allocated seating is a possibility in the short/mid term future.