The next one in the order of the random generator, which I a know a prior as you admitted below.
Say you have money to buy 2000 shares and there are 1000 honest ones, so it's a 66% attack.
That 66% is not necessary. I only need to buy a small minority of the SH (if the total # of SH is much larger than the # of TBs in a CB) and place them contiguously in a CB period, to disrupt the network for a significant period of time. During that time, I control the network and I can use that temporary (but significant enough in duration to cause serious pain to) control to leverage up my financial power to gain more control. I can apply that leverage both inside and outside the protocol of Decrits, to game financial opportunities both inside (e.g. take all tx fees during that period) and outside (e.g. charge an extra fee to those who want add a SH or send any transactions during my control period).
You buy one, the probability of you to not be the next is 1000/1001.
Incorrect. No matter what randomization function you choose for #4, I can game it to place my SH in a contiguous order at some CB period in the future. Because the input entropy is deterministic in some way.
If I can always be next, I will always be next. The more often I am next, the more often I can get the ID that is next (or not so far from next).
No, because you'll quickly deplete your funds, they'll all be locked in shares that you deposited while gaming the order of TBs before. When you'll have no more money, you'll have no further control over the order of TBs, but the honest SHs keep arriving.
I explained in this post and the prior one (in reply to Etlase2) that having contiguous control leads to potential opportunities to gain more income.
Also I explained that just disrupting the network might bring financial return in some other way, such as raising the value of a competing currency or winning a war by shutting down transactions for periods of time.
Also with the power of banking of savings. If I can get other Decrit holders to deposit their Decrits in my bank, I can spend (invest) them interim, while they are not being spent by the owner. The SHs have to profitable and return on investment, else no one will be a SH.
Because I know it before I do my deposit transaction, so I can target being next (or not so far from next). The more I populate my SHs nearer together in time, then more I can control the TBs and control my ID and thus control that I am nearly always next with my SHs.
Only assuming the infinite ability to create SHs, which you can't - there's simply not enough money in the system for that, it's a finite amount at given time.
Increasing the share amount and deposit locking time will make the power even more limited.
I already explained why I don't need to control all of the SH to disrupt and attack.
I already explained how I might gain considerable resources.
And you can't increase the deposit locking time too much, otherwise honest SHs will be disincentivized from participating.