This is my ViewingDale in action on this guilds community world (http://www.youtube.com/watch?v=qELcbKXdRm8). I think you might also want to look at Fractal Mapper 8 or FM8 as its know which does a similar thing. There is also MapTool the VTT which has long zoom in it too.
You can use vectors and technically it would do what you are asking but if the intention is to zoom such that a lot of your world is so small that the vector app would not want to show it then you would quickly find that it uses a lot of memory and takes a long time to redraw it even though its not going to display most of it. The apps above are optimized so that it fades out really small stuff and keeps the speed up - known as the management of Level Of Detail or LODs. If it does not do that then its holding the whole worlds worth of detail in memory at once which will get progressively worse with more detail added.