I had similar thoughts in the past. I kind of expec(ed) that some old Bitcoiners who would like the project might have agreed to ‘create’ a bottom somewhere, and possibly, also sell to earn back their investment after creating such a bottom. Where that bottom would be, remains anyone’s guess. In your experiment @Tromp you set the border quit tight, but like you also point out it could very well be these whale(s) buy in a flexible range in which case few would notice or suspect. It could also involve a collective of old Bitcoiners, making a clear bottom even murkier and being more decentralised.
Actually, there are more ‘interesting experiments’ or manipulations to think of.
For example:
1. The secret benevolent whale(s)
A benevolent whale buys the market, creating a bottom in a flexible range, no one knows the experiment is going on, the result should be a somewhat stable coin, at least around the bottom. Indeed, since the supply is not controlled, the price could go up, the whale might for some time be able to cap the price by selling what they bought while creating the bottom. Since no one knows, the price will go up less quickly I would expect. The result would be at least a plateau around the bottom at which time Grin would be a rather stable coin.
2. The public benevolent whale(s).
Simply by promising to buy for a certain price, the whale(s) create a buy back guarantee, meaning a lot of investors might buy that were waiting on the side-lines since they are near certain not to lose unless those whale(s) break their promise. The interesting part is that here the ‘promise’ is enough, the whale(s) might actually not even have to intervene or spend funds since it becomes a self-fulfilling promises.
3. The secret benevolent Whale(s) want to speed up the bottom
In this scenario, whales do not want to wait for a natural bottom to occur, they simple enforce one by buying Grin high in the earlier years and selling in the later years. In this way a bottom can form earlier which is not completely natural, but which might give Grin quicker some stable properties earlier in the project. If plaid well, the whale(s) might actually not lose money, since they can buy back Grin very cheaply by making the bottom a bit flexible, so going down slowly, while buying back their earlier losses. I am not 100% certain, but I think a similar scenario can also be used in a malicious way, see next scenario.
4. The secrete malicious whale(s)
These whale(s) artificially dumps the price aggressively by selling early on bought Grin.This can actually be beneficial to these whale(s) if these whale(s) can keep up the impression of Grin dying, by slowly letting the bottom of the market drop and by timing well with a Bitcoin bear market. They could create a unnatural artificially low bottom price while buying back more and gaining a unnatural large amount of Grin in the meantime. This would somewhat disturb the fair supply of Grin on the short term but can only be done so long. In any case, the 1 Grin/second rule will mean these actors will slowly lose their dominance in holding. Also, this trick probably only works ones or twice I suspect. If these actors have patience, it might turn them a nice profit in let’s say 10-20 years from now.
5. Many opposing actors (most likely what is going on in reality 
)
Another interesting though would be that many opposing actors might be working on the above scenarios. Most likely some of them have more limited budgets, meaning the end results would be rather unpredictable. In any case, if a benevolent actor is present. They do well to keep some reserves in case the price is dumped to much artificially by a bad actor, to buy back there and make the malicious actor lose money.
For a malicious actor, there is a huge risk if a benevolent actor buys his ‘death scenario’. In this case that actor would lose significantly since he bought high and sells low.