Asking this question just to simply combine opinions for my Productions So I myself and other Creators can be ahead of the game!
One basic about human behaviour (in groups on an average), it seems to move in waves or stay at a fixed point (if you plotted it on a graph). I think we have maxed out our aggression in this music, so i think it will (depending on how society changes):
a) stay the same at this fixed point with aggression being the main driver. (possibly having new types of rap branching out)
b) move towards a more mellow sound, eventually in a couple hundred years reaching "sweet as a rose" rap then bouncing back again
c) the old aggressive rap will "die out" and a new thing will take it's place.
The lyrical complexity is still developing, rhyme schemes are getting more complicated (on average), along with metaphors. So we will see a gradual movement towards complexity on that front till we reach the limits of our capacities.
The pop front of rap is probably going to stay the same (i'm guessing) seeing as it's working fine for them.
One thing i've noticed is a big shift towards people trying to stay independent now, so record companies might start to suffer in 10 years and pop music might actually start to decline.