It would be a huge upgrade, doubling the number of trains passengers from north of Crewe can use to connect to other services at Crewe. This alone would be enough reason for me to fall in love with First Trenitalia if they do it.
I agree that more capacity and more journey options are needed from Crewe northwards, but I suspect that stopping the current Euston-Glasgow fasts is not likely to happen./snip/
Would be of great benefit for plenty people with the extra stopper at Crewe all for 3-4 minutes of time.
When the current timetable was introduced they were severely overcrowded south of Crewe, and in response to protests about the situation Virgin simply withdrew the Crewe calls.
I think doubling the Birmingham to Scotland service frequency would deal with the problem, but suspect that initially the demand would probably be satisfied with trains rather shorter than the current 11- or 10-coach trains. (There probably isn't anything like the level of suppressed demand as exists on TPE trans-Pennine routes.)
Which TOC/Franchise would run them, how they could be pathed and whether they needed to run north of Preston are open to debate. A new hourly service of Birmingham to Blackpool (or Lancaster) EMUs would be a good start...