Whilst a significant number of XC passengers change at Birmingham, there are also a significant number who stay on, and I'd be concerned if all the Manchester to Bournemouth through trains were stopped.
I don't see that there are the paths or platforms at New Street for any additional electric trains from Manchester, so what if any new electric trains were additional and only went from Manchester to Wolverhampton? There are already plenty of trains between Wolverhampton and Birmingham, such as the Liverpool electric trains as well as the existing XC ones, so passengers could change at Wolverhampton if they hadn't caught one of the direct/ existing XC ones.
I know it's not ideal, but the XC trains through the central core of their routes are chronically overcrowded - and only 4 or 5 coaches. This doesn't make best use of New Street's limited capacity at all.