How can an online wallet NOT store the keys? Or did you mean some sort of block explorer? Then again i'm not a very versed person as far as blockchain tech is concerned, but regarding the second sentence i suppose that my 2 GridSeeds that pull a whooping 750kH/s (about your average gamer's GFX card scrypt hashing power) don't allow me to participate in mining. Or, wait...!! I forgot that i'm not a regular consumer, i actually run an industrial mining farm with said equipment. I also run a PoS coin full node with an average of 40 active connections, and i stake once or twice a day (which thing is possible because the userbase is SMALL; with a userbase bigger than 60x24x365 (about half a million - negligible) i would be lucky if i staked ONCE per YEAR). But then again, a staking pool doesn't need the user's keys or coins... what for?

EDIT: I can see a "staking pool" working with just a regular account and a public key holding the coins, but that would be based ultimatelñy on trust - i.e. the user has your word that they will get paid for having coins. But what about change addresses? What would happen when a fraction of the coins are spent? How would the "mining fee" be collected? If you can really pull this off i'll be a bit impressed tbh, but it will still be completely centralised.

EDIT2: I know that the "Growth Account" would require you to actually store the coins in their wallet, but i assumed that this should have been a deal breaker in the first place. There's no decentralised network unless you run your own node, and with an initial userbase of 1MM average time between rewards is roughly 2 years. THAT was the technical innovation i was looking for (keeping 60 seconds block time BUT achieving a workable reward system). But then again YMMV.