When t3 was divided into two separate dungeons, it made the raid more workable and available for puggers and for smaller guilds. The vast majority of t3 pugs on Set are for upper or lower t3.
I suggest that T4 be broken up into two separate raids:
General through Zodiac as one instance
Emperor through Entity as the other
Then you only need two instances.
Benefits:
1. Lets more pug t4s get set up, as players are not going to be stuck in a pug t4 for six hours or days to try and finish it
2. More pug raids would likely be formed, just like what happened to t3, because people would not be locked into a full day but would have a chance at a couple hour raid to get through
3. T4 guilds could cycle more people through the last bosses as was designed by Funcom so more people would get the t4 gear and more options would be done for gear
4. One argument before was that no one would do the smaller bosses: does anyone worry that the Basilisk might get lonely if no one attacks it? Plus it opens up lower t4 for pug raids, which are very rare right now on Set (t4 anyway).
But you rarely see a full t3 pug raid on Set (RA did one on Sundays but mostly filled from guildies) the vast majority posted for pugs are lower or upper t3s since its a time factor.