Having access to the draw loop (like in version 1 of Maps) would be wonderful too, but this would probably suffice for most things.

It is possible to generate a Bitmap for each marker. 
You only have to create a canvas backed by the source bitmap you wish to customize or by a transparent bitmap and you can do your custom marker just as before. 

I think the point of the OP, though I could be reading it wrong, is to be able to dynamically change what's drawn on the marker.

If you wanted a character on the map to 'walk' across the map there isn't really a practical way to do it that I've seen. Short of making a marker for each step of the animation and then cycle through each marker and update the visibility and location of each.

Yes being able to dynamically change markers without adding/removing would be great. It would also help with pin clustering in my application.

@2: have you tried it? I use that technique but sadly am blocked by leaks ( issue #4703 ).

A subclass-able marker could suffice but a callback might do as well:
We could have a callback optionally set on the map, to permit us to draw our own markers. Ideally we would be passed the locked canvas, the screen X,Y where the marker should be shown, a scale factor (to account for 3D perspective in the projection) and of course an indication of which marker is being drawn. 

 Issue 5600  has been merged into this issue.