Bus stops here: Shanghai lets riders design their own routes

Sounds like minibus in Hong Kong with extra steps - we have been doing this since eternity. Driver just ask where people would stop in advance, sometimes an entire area would be skipped if no one goes there

How does that work out for someone in the unpopular destination who wants to leave?

There is a loosely defined route that still needs to be followed. You just shout you want to leave when you are near your destination. Or the driver would ask/shout is there anyone going to XXX area when it is near, you are supposed to say yes otherwise it gets skipped

I guess I’ll add an example. Let’s say the minibus mainly goes from A to B, but pass through C in the middle. Dropping people off at C is often a non-trivial task that may takes a couple of extra minutes so you need to tell the driver in advance

No, I mean, what if there is someone at C that wants to catch a bus, but all the buses are skipping C because no-one already on the bus wanted to go there?