It's certainly possible. Maybe I'm too optimistic, but my hope is the expense to the user up-hubbing results in some restraint. Whether it's credit I've received or paid for, I'll think twice about sharing a cute picture of a cat or up-hubbing a witty but low effort comment. In a world with no down votes, having a small expense to sharing a link hopefully steers users toward posts they find valuable rather than merely amusing.
I thought about this too but couldn't get past the "pay to win" model. If, for example, hubski gets super popular, what's to stop an ad agency from buying 1,000,000 and flooding the site? Credits are cheap and $5000 is a drop in the bucket of a major ad campaign.
What's stopping them from creating a bunch of accounts and doing that now? These bits are buying you anything. We're not saying you can't share if you don't have money. Interactions are remaining the same but now your vote has a bit more value.
Oh, I was replying specifically to the idea that submissions should cost some nominal amount of bits.
Honestly, it could work really well, I'm merely trying to express my fears. I hope that the system goes exactly how mk and friends have planned, I'm just a bit too cynical. If this system went live, I would certainly buy in for a small amount just to feed the system and support hubski.