Actually this is something that concerns me far more than the initial distribution or the PoS reward for forging.
If AE bid/ask tx's can be arbitrarily included or not in a block then I can see a lot of manipulation occurring in this part of the system (another reason that I am not really hooked on the whole AE thing).
This of course could be compounded by huge stake holders "colluding" to say hold back orders.
Luckily Nxt can't provide HFT so we shouldn't worry much. Time critical trades will still be done off-chain.