The trouble is that one reason Merseyrail is a reasonable TOC (I'm not going beyond that, as I certainly do believe they have more issues than their fans would like to suggest) is that it's dead simple. Everything all stations[1], very near to being fully clockface, one class of EMU (OK, technically two, but they are basically identical), only a small number of depots, everything third rail electrified, simple ticketing (just Anytime Day Single/Return and the day tickets plus PTE stuff), all suburban demand profiles etc.
If you start running them all the way out to Wrexham, that really complicates things. It's one reason I think they should only go as far as Burscough Bridge, not Preston. Indeed, the case is quite similar between the two - but then add to that operating into Wales which has some different legislative matters etc.
I'd leave it with the Welsh operator but run it into James St spare platform.
[1] Yes, Capenhurst - but I think we will see those stops back in with the 777s.