Now that seems like an interesting lost feature. Any reason why it was removed? How was it exploited?
It had its bad sides.
1. You could never tell exact moment when that timer was ending, so the person that entered had an advantage. Using BG, he could run to you and just burst you after his timer has ended. If you shot at him while he had timer on, you've lost Action points. Also, if a group entered then 15 seconds was enough to take good positions - sometimes even in building, like in Modoc, for example.
2. As mentioned above, losing Action points was extremely annoying.
3. Some people used it repeatedly just to enter the map, shout some insults at you and then run to the grid.
4. With a bit of effort you were able to block someone that was just running to the exit grid (making him "moon-walk" or just making his path longer, also in theory, while he was loading the map you could surround him with people).
5. Sometimes combination of being spawned far from the exit grid and time of loading the map + a bit of lag was making you dead, because grid campers could already shoot at you and start your combat timer.
Still, it was a lot better than preview, because you were unable to scout the map from the worldmap. If someone scouted you, then you could prepare for a possible attack. Now you don't know when someone is scouting you and usually you don't have an idea how many people are using preview. In addition to that, when you were leaving the map, due to "broken" tracking system you could see who is on worldmap nearby. So basically, there was no option to hide on worldmap completely, while now you have spy-satellite tool while being completely invisible and grid camping changed to worldmap camping. And then, some people want be able to refresh preview via a button.