People will feel much more comfortable sending money to regulated exchanges run by people who know what they're doing and backed by venture capitalists (remember that NYSE recently invested in Coinbase) with a big stake in Bitcoin. The amateur exchanges will either professionalize or be left in the dust.
In my view, this may well be the biggest news story in a long time.
This will be a game-changer. But both, Gemini and Coinbase will be limited to US only. So all the other 'amateur' exchanges will remain a decent market share and will have some time to re-think their long term strategies.
Bitstamp will be the one that have to adjust quickly. Wouldn't be surprised if they implement other fiat/crypto currencies. They won't last long with one BTC/USD pair.