First of all, it depends on what type of gateways we're talking about. Gateways for BTC, BTS are well and good, but what we really need most of all is on- and off-ramps between BitUSD and fiat. I can't think of anything else (except for perhaps a stable client and good user experience) that is more important for BitShares' success. It's the BitUSD/USD ramps that BitShares desperately needs to tap into the mass market, appeal to merchants, and achieve a huge network effect. Marketing is also important, but marketing by itself doesn't guarantee victory--just look at Bitcoin, which, despite receiving a ton of mainstream media attention (e.g., the recent Bitcoin Bowl) is still only used by a tiny fraction of the population. But good marketing + robust fiat on/off ramps? That would be an awesome combination that would be a nearly sufficient condition for BitShares' success, IMO.
Overall, I'm in favor of establishing gateway-focused delegate positions because it's easy to underestimate the risks, costs, and time involved in setting up a strong fiat gateway. It's not just a matter of technology development; there are KYC and regulatory issues as well. This is clearly hard stuff. If it weren't, no doubt Bp and others would've announced multiple deals and partnerships by now. So, sufficient incentives need to be in place for exchanges or other entities to take the plunge and be the first to develop the types of gateways we need. We could always try asking the Coinbases and BitStamps of the world nicely, but I doubt that by itself will be very effective.
Gateway-centric delegate positions could (1) serve as a reward for creating and maintaining BitUSD/USD gateways or (2) provide a mechanism for funding a pool of free samples that can help encourage exchanges to try BitUSD. IIRC, that's how Ripple got BitStamp to become a XRP gateway--they gave them a bulk amount of XRP upfront.
This area of infrastructure development should be made a key focus of BitShares NOW given the substantial time lag that will be needed to develop a robust system of ramps and gateways.