I'm gonna say that if the 1990 by-election had never happened, the line would look like this today;
The line would have been electrified between between Four Oaks and Longbridge at the same time as the West Yorkshire electrification with the work being finished in about 1997. Electrification had been talked about for many years, so there was some political will for it. The line would not have been electrified to its terminuses becasue it would have been funded partly by central government and partly by Centro. Staffordshire and Hereford and Worcester County Councils would have had no part in it.
I'm guessing that the slam door DMU would have gone by about 1995. The government would have ordered extra Networkers (150's had stopped being produced by then) to go onto the Snow Hill Lines so that they could opperate out of Tysley depot along with some of the Neworkers used on the Snow Hill - Marylabone service. The 150's from the Snow Hill Line would have then been cascaded onto the Cross City Line with any left over heading up north or to the South West.
When electrification started in 97, slam door electric rolling stock would have been cascaded from the South East to run the Four Oaks - Longbridge trainds and these would have been replaced with 333's (ordered alongside those for West Yorkshire) in about 2000. These would also have replaced slam door electric trains on the Wolverhampton - Coventry and Birmingham - Walsall services.
Some extra 150's may have been cascaded from the Chase Line and possible from the North of England to provide extra rolling stock for when the service increased to 6tph in 2004, at which point Chase Line trains would have gone over to 170's.
So today, there would be a 2tph Lichfield Trent Valley - Redditch and Lichfield City - Longbirdge service opperated by 150's (about to be replaced with 172's) and 2tph Four Oaks - Longbridge opperated by 333's. That would probably cause a few capacity problems because I'm guessing that with 150's some peak time trains would be formed of 4 or 5 coaches when they ideally need 6.