'cannot be sold' but BA are not selling them, they are just regaining them. I would imagine anything goes once they have them back.
Lets be clear, BA are only regaining them for certain for W15. They are available for any other airline as follows
The Trustee will open the applications process for the IATA Summer Season 2016 on 23 July 2015. Applications for slots for Summer Season 2016 under the Slot Release Procedure of the Commitments must be received by the Trustee by Close of Business (COB) on Thursday 20 August 2015. The COB deadline for applications is 6pm British Summer Time (BST). Applications received after this deadline will be rejected.
Under the Commitments, Applicants are entitled to apply to operate the following city pairs:
London – Aberdeen
London – Edinburgh
London – Nice
London – Cairo
London – Moscow
London – Riyadh
At the end of the IATA Summer 2015 season, 9 slot pairs used on Edinburgh and Aberdeen will be returned by the carrier that was awarded these slots in the IATA Summer 2013 season. For the IATA Summer 2016 season, 7 slot pairs in total will be available on London Heathrow-Aberdeen and London Heathrow-Edinburgh. A further 5 or 6 slots pairs (to be confirmed pursuant to clause 1.1.1(b)) in total will be available on London Heathrow-Nice, London Heathrow-Cairo, London Heathrow-Moscow, London Heathrow-Riyadh, London Heathrow-Edinburgh and London Heathrow-Aberdeen. The details of the application and selection procedure are set out in Clause 1.4 of the Commitments.
Don't jump the gun just yet I believe at least one airline sniffed about for them
Ex