I don't think people understand how Market Cap works...
Take people saying Ark for instance. Even if you give it Ethereum's $24,000,000,000 market cap and a price of $0.40 (half of what it currently is), you'd still only obtain a ~600x (6000%) increase. I say "only" because you have other coins that can still do much better than that at MUCH more reasonable market caps (lets face it, most coins aren't breaking the $1,000,000,000 barrier anytime soon).
Look at Tokes. Even if you only give it a market cap of $1,000,000,000 with it's current price of $1.50, you get a return of ~1000x (10000%).
Now, will Tokes ever make it to that market cap? Maybe (if they can deliver on their roadmap). I'd say it's way more likely than something like Ark reaching Ethereum's market cap.
My longshot picks would be Tokes, Dnotes, CloakCoin, and ZenCash. They can get a 40x-90x return if they ever approach top 10 status (Tokes being the ridiculous 1000x dark horse), are all available on decent exchanges (Poloniex/Bittrex), and aren't completely useless/obscure.
Etheroll is up there with Tokes (1000x) but honestly I'd see Tokes getting there first. Etheroll was a good proof-of-concept but it can't compete with the other gambling sites and suffers from still not being on a popular exchange. I'm not sure it has much of a future IMO.