Exchange-traded funds versus mutual funds: The former is the new kid on the block (20 years old this year) that's been the hot investment product of the 21st century with sexy offerings that target ever-narrower slices of the investment market. The latter is the doughty stalwart that's been around for seven-plus decades and is seen as a tried-and-true 20th-century investment vehicle.

So it seems logical that when a handful of top ETF executives sat down together on a conference panel to discuss the state of the industry and its future, that somebody (in this case, the moderator) would ask whether ETFs will displace mutual funds in a huge portion of investor portfolios.

The answer, of course, isn't that simple. "It's difficult to make a comparison between ETFs and mutual funds because they don't have the same investor base," Joel Dickson, Vanguard's senior investment strategist, said today at the IndexUniverse Inside ETFs conference in Hollywood, Fla.

What the panelists agreed upon is that the fast-growing ETF business still has plenty of room to grow. One of the things they didn't agree upon was what kind of inroads ETFs will make in the market for actively managed funds.

Micahel Sapir, chairman and CEO of ProShares, noted that just 3 percent of U.S. households own ETFs and that less than 50 percent of financial advisors use ETFs on a regular basis. Despite the relatively low penetration rate of ETFs vis-a-vis mutual funds, he believes investors already have reached a verdict about where ETFs fit into a portfolio.

"When it comes to active versus passive, I think ETFs have won the passive game because most investors see it as the superior way to gain exposure [to passively managed, index-based offerings]," Sapir said. "There are about the same amount of assets in mutual funds and ETFs that use passive strategies.

"The big question is whether ETFs will grab more of the active market," he continued. "That's a challenging question because to a large extent the reason why ETFs have been so successful is due to their underlying passive strategies."

Sapir said that ETF products began with a focus on equities, and then evolved into other asset classes including fixed income and commodities. He offered that the next big opportunity for ETFs will be in alternative investments that include managed futures, private equity, long-short and hedge fund replication strategies, among others.

Many—but certainly not all—ETFs that offer alternative strategies are a hybrid in that they passively follow so-called active indexes (i.e., indexes that don't employ passive market-cap weightings).

"I think there will be moderate, but not overwhelming success [in actively managed ETFs] like we've seen on the passive side," Sapir said.