Well, a lot of people will make money and a lot people will lose money. It will be interesting what happens when some ScamCoins go to zero. Eventually there will be some solutions.
Any coin which does not have enough mining power to be secure should not be listed, as listing it is basically simple a scam to scam people who do not understand how blockchains are secured out of their money.
This is a judgement by one person (not the market). If you're right with your judgements you can make money in the market, and the market as an aggregate will be either right or wrong. But some groundrules for altcoin exchanges might make sense. Say exchange A allows all coins, including ScamCoins and exchange B limits itself to a certain set. If B's scheme works better people will realize this over time.
I don't see how the hashing power argument could be formalized, so that they are not debates around it. Opinions vary a lot. For instance this would mean Proof-of-Stake = Scam, which I would not subscribe to a priori. Also I'm really sure it makes sense to speak of mining power per se. Any future alt-coin IMO would have to break the mining power, so that the old hashing power becomes not applicable.
The only rule I can see which is obvious is the opensource requirement. One can think of many others. At some point there will be probably be same kind of layers similar to stock markets.
Buyer beware as with anything in life. If people do not take some time to research then they deserve the results.
Sounds like the guys at Goldman Sachs. I think we can do better than that. Not by regulation, but by using trust protocols.