I'm not convinced by these 168 rumours. To introduce them would undermine Wrexham and Shropshires 'offering'. These currently places emphasis on high quality travel environment, buffet service, full catering in first. It makes sense to trade on these qualities as clearly they can't compete on speed.
Introducing some services operated by 168 would undermine this, and make it much harder to articulate to the public why they should travel by WSMR, and therefore make it harder to successfully market the service.
However I guess there is scope for peak loco hauled services to now operate under the WSMR banner, with less busy ones operated by Chiltern on a 168. Have to say though that such a long journey on a 168 isn't very appealing.