IMO steemit is already dangerously close to a ponzi - it doesn't generate (monetary) value, but it promises to pay out monetary value. The only way these payouts can work is that there is simultaneously a sufficient influx of monetary value into the system, and the only driving force for that influx is the promise of higher output through higher voting power.
Your Dreamcoin is NOTHING BUT a ponzi. At least steem can hide behind phrases like "steemians create valuable content". Dreamcoin promises high output, and the only way to maintain that output is to attract people by making that promise. It is inevitable that at some point the number of people trying to cash out will be higher than the number of new investors, at which point the whole scheme collapses.
I understand why you might think that, but let me break the concept down for you:
Assumptions:
At no point is anybody else's unsecured money involved.
If other copycat speculators attempt to do the same exact thing with their money, they are the ones taking the risk providing the same valuable service.
In the end, if any such service provider falls by the wayside, they are the only loser, since the system will do an automagic margin call and return full value to the holder of each and every dreamcoin.
The appreciation effect caused by the whale's investment is an identical calculation to Disney World buying up vast tracts of swamp land south of Orlando. Their own continuing investment drove up the value of the land they purchased helping to offset the cost of providing a theme park and all the other elements of that ecosystem.
The hypothetical whale is just guaranteeing via counterparty free smart contract to share 5% of the hoped for annual digital real estate gains (whether they are realized by the whale or not) with users of their innovative product.
There's such an obvious, huge difference between Dreamcoin and Disney that I can hardly believe you're bringing that up (and in my experience, seemingly huge but weak and illogical comparisons are typical of ponzis): Disney has not just bought land and thereby magically increased its value. Disney built a theme park. Theme parks attract tourists. Tourists bring money with them. Tourists with money attract merchants. That's why the ecosystem in Orlando grew. The most important point though is that Disney is not continuously pumping money into that ecosystem, they're drawing money out! They have created something that generates value.
Dreamcoin OTOH builds nothing but a speculative bubble. Dreamcoin promises exponential payouts (which is typical of ponzis, too). You cannot generate exponential payouts without an equally large (i. e. exponential) influx of value. Your plan is to back the payouts by creating a speculative bubble, but at some point that bubble will inevitably pop, and then the whole system crumbles into pieces.
Another typical trait of ponzis is that the risks are being downplayed. Margin calls can only execute if there is sufficient liquidity on the market. When a speculative bubble bursts, the result is usually a price crash. This will trigger so many margin calls that they cannot all be filled by existing orders, which means that Dreamcoin will end up in a black swan. Black swan with panic sells of the underlying collateral means almost complete loss by dreamcoin holders. That's where the risk lies.
Disney's continual promotion and upgrade of now three theme parks on that land plus multiple hotels and a nearby cruise lines provides an ecosystem that has attracted uncountable other businesses to the local economy. Since the net result is very profitable to Disney they will no doubt continue to work to grow it in perpetuity. Synergies abound with third parties everywhere.
The BitShares ecosystem is no different. Just substitute worthless ledger entries for worthless swamp land and the analogy is perfect.
Sure, the Orlando economy could crash if Disney pulled out. Someday it could all be a ghost town. That doesn't mean that businesses and tourists haven't derived mutual benefits from the ecosystem for half a century.
Even if Disney pulls out the theme park will still be there. That's the point - they have built something that generates (monetary) value, whereas Dreamcoin does not build anything. It just creates a bubble.