Purely speculation - 180's have been mentioned. However, the IEP's arent ready for service and wont be by july so theres little prospect of releasing the 180's.
HST's are a possibility. They are the only other 125mph traction in this country, however again the IEP's arent yet available for VTEC so therefore the HST's cant be released.
442's have been mentioned and much has been said about them in this forum, both good and bad. They are however now being released and would be available. With both 67's and 68's available to pull them there has been genuinely serious internal considerations of their use and DRS has been suggested internally as the haulage traction provider. These could potentially sustain 110mph running on the ECML. Nick Donovan told me that during the 3 peaks challenge. However, realistically the modifications required and clumsiness of operations may well render them impractical to use.
319's are now being released from GTR. Moving to northern would start a cascade of 156's which could release 158's which themselves could free up 185's destined for northern connect to remain with TPE for now until the new TPX units are built, or the 158's could make reappearances on LIV-SCA services (TPE Scarborough crews sign 158's anyway)
In all cases however there is a significant lead time, employment of the pretendolino has also therefore been suggested to free up 2 185's from the scottish route, but again, theres no guarantee GA will have finished using it in time. Coupled to an 88 or a 90 theres no reason however why this cant run at 110. Problem is we still dont have any 88's!
Internally however, very little has been said, and with just 6 weeks to go before handover, the lack of communication isn't doing staff morale any good at all.