Yes, the biggest change for late 2016 or early 2017 will be the new light rail line to DIA (Denver Airport). This will bring more traffic to Union Station and create an easy plane-to-train transition. But there are already several light rail lines you can use from Union Station, as well as a very large and convenient bus terminal in the same building. The busses (RTD) connect to the larger Denver Metro area including Boulder, Longmont, DIA, etc.
If I may make a correction, the rail line to DIA will be heavy rail, not light rail. The difference is that the 3 northern lines will be "commuter" rail lines running reconfigured versions of SEPTA's Silverliner V EMU cars. They will have high level platforms and greater stop spacing than the light rail lines, With the planned service frequencies I recall seeing, the new lines will qualify as regional rail lines with 7 days a week regular service. Whereas to me, commuter rail means heavy rail lines with schedules that are all or mostly aimed at taking commuters downtown on weekday morning, back home in late afternoon and the evening with little to no service outside of work hours.
The expansion of the Denver rail transit system in 2016 and then 2018 will be one of the largest and quickest expansion of rail transit we have seen in the US in decades. Only Los Angeles has as many new rail transit lines under construction.