Scotrail's inheritance of HST sets to be delayed by 3 months due to the Great Western electrification being also delayed, so they can't be released from that service.
Alastair Dalton make a reasonable stab at linking it to current issues affecting Scotrail but I think the 2 are fairly independent issues and 1 won't solve the other. The HST sets are all about increasing long distance comfort, not necessarily increasing capacity (although they are releasing Turbostar sets I can't remember if these are to be cascaded on to other Scotrail routes or will head South in exchance).