There was a concept I thought was neat. Imagine around stops you had a parallel set of tracks with cars that would connect to the train and passengers would have X number of minutes to transfer between the parallel trains before they decouple.

So a ‘fast lane’ train wouldn’t actually stop, it would just couple to another train that does pretty much nothing but transfer passengers to and from the stop.

Though the reality is that would require a lot of work when the counter argument can be “fly a plane direct instead”