Northern Rail is a loss-making TOC that despite supposedly rising passenger numbers ('exponential rises' have been claimed here), continues to plan for 2 & 3-car trains that are supposedly loaded well in excess of capacity, (cue anecdotal reports of single Pacers with 250 on board), yet seems to have no enthusiasm to make their services fit this demand by having platforms capable of the 4 and 8-car trains that would be available to them. Surely the 'Northern Powerhouse' could justify a proper railway rather than hundreds of branch-line length trains, each with driver and guard/TM working them.
Unless there are specific geographical impossibilities, any station that is expected to handle large numbers of commuters of day passengers should be planned for 8-car or longer trains. I'm sure that if the DfT said that they could have enough new 4-car Electrostar EMUs on all these routes, something would happen fairly quick.
319s, like 321s and 455s are run in large numbers in the south-east. They do have problems with poor railhead conditions down here, especially in the leafy suburbs where local resistance to tree lopping often results in more leaf problems than should be the case. Most of the year they just get on with running the services.
As far as acceleration goes, it's true that the MKIII EMUs are not the fastest around but they regularly run in and out of 100-125mph stock on really tight headways and all the 8 and 12 car trains are really full! If the NW trains were longer, some of them could be dropped maintaining the same service capacity thereby releasing more paths and/or increasing headways - especially if the 'Northern Powerhouse' isn't all that the politicians have promised it to be.