"People are still confused about what will the final hybrid be, who will be the players," he said. "What is truly going to be the floor brokers' role, what is truly going to be the specialists' role?"
But that's not the only problem.
"The view some people have is once the hybrid and Reg NMS come to market, it's only a short time thereafter where the majority of order flow goes more toward the Arca (Archipelago) model or electronic execution model," Mr. Rodriguez added. "The question is, is it going to survive, and if not, why should I spend too much time thinking about it?"
Reg NMS is the SEC-mandated market structure rule that was passed in April 2005. Major portions of Reg NMS that require electronic connectivity between exchanges and other liquidity pools and favor automatic execution platforms are scheduled to be implemented later this year.
But officials at the exchange, now known as NYSE Group Inc., are not letting the naysayers influence them.
"We're focused on hybrid," said Gerald D. Putnam, president and co-chief operating officer at NYSE Group. "We're spending a lot of time on it. It's a major project for the NYSE."
Mr. Putnam, who was chairman and chief executive of Archipelago Holdings Inc., Chicago, which the NYSE acquired in the deal that took the Big Board public March 8, said officials are listening to critics who charge that the hybrid is too complicated. But they are not considering changing course.
"We'll build something I think is going to be an improvement for the NYSE marketplace and a good solution for our customers," he said. "We're not going to do the wrong thing."
In the middle of December, the exchange began its pilot program for the hybrid, opening a few stocks to the blended system and by March 10, about 150 stocks were trading on it.
Mr. Putnam said the experience to date was promising, with good feedback from brokers and specialists on the exchange floor.
"We're looking to expand it," he said. "We want to get this (version) rolled out across the whole floor so we can move on and add the specialist API and other ‘go-fast' aspects of the system." (The specialist API is the name for trading algorithms specialists will use.)
Sang Lee, managing partner at financial consulting firm Aite Group, Boston, questioned how valuable the pilot program has been for institutional investors.
"A lot of this they're testing really just for floor brokers," he said. "The hardest part of the platform hasn't been tested — using specialist algorithms, testing what the specialist can do on a manual basis."