Microsoft has not given a date or time frame on when new hardware will be out.
You will not see as many hardware updates to the Zune product line as Apple and other manufactures. They are putting their efforts into making the software better so you dont have to keep purchasing new hardware every year. You have to admit that it is pretty bad ass for the earliy gen 1 adopters to get a brand new like device with every major firmware update.
So if you want a Zune buy one cause the waiting game doesnt work too well in this case.