Thus far I've maintained a dignified (?) silence on this topic, but it has got to the point where I can resist no longer.
My background is that I was heavily involved in both the infrastructure planning and timetable development of the West Coast Route Modernisation. Some key parts of the design exist because of ideas I had, arguments I put forward, and designs I helped to develop. Once WCRM had reached its natural conclusion I moved on to HS2, where I was in the first 10 people in that project, and worked on route development, timetabling, and many public consultation events, before taking early retirement.
The West Coast timetable - as stated above - took a small team of people about 3 years to develop from scratch, dealing with an ever-changing infrastructure and linespeed profile, and a "benevolent tyrant" at the DfT in the person of Stuart Baker, who oversaw much of the work from the Government's viewpoint. When you make trains run faster, journey times become shorter, and more people are attracted to rail. That generates more revenue. Thus improving a railway can be largely self-financing. Conversely, if you slow the trains down (e.g. by inserting additional stops) then revenue is decreased, because the extended journey times make rail less attractive. As explained already, increasing the journey time can also result in additional sets being required. The existing London - Manchester trains have turnround times of around 20 minutes at each end of the journey. Each additional stop will cost you 4 - 5 minutes in time loss decelerating + dwell time + time loss accelerating back to line speed. The turnround times are currently adequate, with a small allowance to absorb any late running. Add any additional stops, and you are almost immediately into requiring additional sets in the circuit - and you may also need to build additional platforms to accommodate them. (Oh, but hang on, Euston is having its platform numbers reduced by HS2 works ...)
You can't simply suggest adding another stop without considering the effect on other services on the route. For example the (pre-COVID) WCML timetable had standard hour departures from Euston at 00 to Manchester, 03 to Birmingham, 07 to Liverpool, and 10 to Chester / North Wales in the first quarter of the hour. The stopping patterns on the WCML for each of those trains was arranged to minimise interaction between them.
So let's try adding a Watford Junction stop to the xx:00 to Manchester. What are the effects? Well, the xx03 to Birmingham will take a hit of about 3 minutes, followed by the xx07 to Liverpool which might take 2 minutes, and the xx10 to Chester might catch 1 - 2 minutes. The Liverpool is now following hard behind the Birmingham, so when that slows to turn in for Rugby, the Liverpool will catch another minute or two there. Already we are into an annual revenue loss of many millions of pounds, just through squandering time in poor timetabling (i.e. adding at Watford stop into a Manchester train where it couldn't fit). The West Midlands trains are (or were) flighted 3 minutes behind the Manchester trains specifically because they were both at clockface 20-minute interval departures from Euston, and that was the only way you could fit in all the services required by DfT and Virgin (remembering the history of the former Virgin / Railtrack deal which brought Railtrack to its knees). Remember there are fast line EMU departures for London MIdland to fit in too.
There will be a need for an entire rewrite of the WCML timetable once HS2 opens - or possibly several such, dependent upon the staging. Please let us not pretend that we can randomly insert additional stops in the timetable in the meantime without at least understanding the consequences and timescales involved - and above all the costs.
So if you want to propose to make additional stops on any WCML services - either in the current COVID timetable or longer term (assuming some semblance of a return to normality) then please go right ahead. However I urge you to do your homework first. How will delaying a specific train affect its interactions with other trains on the same route? Will the disbenefit of a longer journey time for all those passengers already on board be counterbalanced by the additional passengers benefiting from the extra stop? How will the terminal turnround times and platforming arrangements be affected? Will the revised path introduce any additional junction conflicts?
Thank you for your patience in reading this diatribe, and I beg forgiveness for any offence caused.