What I want to see in 1.08 is buildings that can be destroyed through war, sieges and events. Now everything gets more and more developed as the game proceeds. A little uncertainty would liven things up quite nicely.
Make decadence for islamic rulers more punishing, harder to get rid off and easier to accumulate. When the desert tribes do roll in, have a realm splinter instead of just replacing the ruling dynasty. It's more balanced game wise and even more historical.
Rebels now are rather boring. Make a player take notice by giving rebels a chance to burn down buildings, have succesfull rebellions given a % chance to spread to neighbouring provinces and add the possibility that a succesfull rebellion either starts a new independent republic, a new independent county/duchy or even spawn a possible pretender all set to take the crown. Also look at the rebels in for instance EUIII with their goals and think of ways to implement this into CKII. Rebellions now are an untapped vessel of possibility and deserves more attention.
Traveling the sea was dangerous in the middle ages. Why not add a chance for your fleet to fall victim to a storm? It would bring some life and excitement to the dull process of moving troops oversea. Naval warfare would also be very nice to make an entry here.
Herecies could use a little more attention. The potential is there to have heaps of fun with them. Crusades, inquisition, bringing down a faith from within, massive religious wars. As is, they are a bit stale.
More plots, decisions and ambitions. As always. Look at mods like CKIIplus to see how much life and personality these bring to the game.
And again, as always, more events. More events is good. Everyone loves events.
