"In the past, employers automatically enrolled workers into 401(k) plans at low rates and workers often wouldn't increase their contributions enough to reach the full company match— to the detriment of their retirement savings," explained Rob Austin, director of Retirement Research at Aon Hewitt.

"Because many employers gauge the success of their plan by the number of workers saving enough to receive the full match, they understand that they need to give workers an added boost by either starting them off at a more robust savings rate or automatically escalating contributions over time up to, or beyond the match threshold. That extra savings can have a remarkable impact on workers' long-term savings outlook."

All of that may sound promising, but according to the Callan Investment Institute's "2015 Defined Contribution Trends" study, which targeted a larger universe of respondents, auto features may have reached their saturation point.

The study found that 61.7 percent of the plans it surveyed now offer automatic enrollment. But only 12.8 percent of employers that don't offer auto enrollment indicated they plan to add it as a feature in the future. Those who don't offer it said the feature was not a priority for them, calling it either too expensive or unnecessary.

In addition, the Callan survey found that auto enrollment is primarily aimed at new employees, not existing workers, so its reach is limited.

Aon Hewitt's survey also found that among plans with automatic enrollment:

• 7 percent default above the full company match level;

• 34 percent have default rates at the full company match level;

• 59 percent default below the full company match level.

Among companies that have not implemented automatic enrollment:

• 67 percent cite the increased cost of the match as the biggest barrier;
• 37 percent are concerned about the reaction from employees;
• 30 percent do not want small account balances in the plan.