This is what happens in Melbourne and it's a non-issue if there are clear PIDs.
The rail network - 16 lines in total - is split into 4 groups and at Flinders Street (which is the origin/destination of all metropolitan train services), groups of lines have dedicated platforms - so regular users know the general platform they need to go to and just need to check where the train is going on all the PIDs on platforms.
Example: the Caulfield group consists of the Pakenham, Cranbourne and Frankston Lines (Sandringham used to be part of it (well still technically is) but it's now operationally separate and has dedicated platforms at Flinders Street) and as a Frankston train arrives at Flinders Street, it might then become a Pakenham or Cranbourne service or vice versa or it might become a "short stop" service (i.e have a destination which is on the Frankston Line but run the stopping all stations services rather than express service) etc.
Likewise with trams - even though there are only two tracks - on Swanston St which is the world's busiest tram line, there are 8-9 different routes running on it, most terminate in the inner north at Melbourne University and then turn back and head out to the south and east again. Like rail, certain routes are grouped and therefore share common vehicles and trams can go into the Melbourne Uni shunt as one route and then start the reverse journey as another.
I have a feeling that this is becoming less and less common on trams as routes are dedicated fleets (i.e larger trams for routes which carry more people) but they're sharing tracks in the city segments, eg. Elizabeth Street trams: 19 (large 5-section trams), 59 (older B class articulated trams) and 57 (oldest portion of the fleet: single car Z cars).
Even though the trams are well branded with their route (front, rear and on the sides of the trams), regular users are getting to their routes by the tram type.
Doesn't happen much with buses in Melbourne as we don't rely on it in the centre of the city (although some of the DART buses which run along the Eastern Freeway may do it - I'm not sure as I don't use those services at all).
Anyhow, yes it can work quite well, as long as the Passenger Info Display is done correctly - i.e the driver needs to remember to flick it over at the right time.
Rail map for reference - Caulfield is where the Pakenham/Cranbourne/Frankston lines all meet in the inner south east:
Tram map for reference - Swanston St is the big thick block of lines:
Linear Mode
