I agree if by "fully legal" you mean completely unregulated, but then nothing is 'fully legal,' so-to-speak
to OP; the first anti-marijuana legislation came down in 1937, nearly 80 years ago--a little more than just "20+ years." The socioeconomics of the issue is fairly entrenched. when you have testimony in the congressional record that cites the contemporary equivalent of tabloid magazines, and when that testimony centers on the capacity for the cannabis plant to make African Americans think they're equal to persons of caucasian ethnic background--a piece of testimony offered as proof of the DANGERS of cannabis--you can begin to recognize the complexity of why cannabis prohibition has persisted--race relations aren't exactly peachy in 2014 USA. Now, add to the racial motivation (the "we-noble-white-folk-must-keep-those-savages-of-different-skin-pigmentations-from-lashing-out-while-on-the-weed" mentality) the steep financial implications to the timber (i.e. paper), petro-chemical, and pharmaceutical industries, all of which were both burgeoning and interested in minimizing any potential competition. Check out the H.J Anslinger-Dupont-Hearst connections if you want to get even more conspiratorial. But I digress.
1 year is likely too brief a time-span, especially when considering it is 2014-15 you're talking about--just before a presidential election; not sure its something the obama administration would want to tackle (immigration looks more likely, but honestly healthcare and military spending are probably even more central to the finish of this presidency). Also, depending on who wins in 2016, you can bet the first thing they're going to do is NOT tackle the war on drugs. we focus a lot on cannabis around here, but there are some more tricky and more nefarious drugs to control for; now, i agree, they pose a problem to around 1% of the population, but still, it'll be something the DEA can argue about (they're just trying to keep their jobs, after all).
I see this being a protracted state-by-state issue. When more than 2/3 of the country have swung to the legalize/medicalize/regulate policies, there will be potential traction for a "grassroots" movement, but now we're talking about a 5 year timeline minimum.
so, for example, lets say the senate approves and president signs the new appropriations bill that prevents DOJ/DEA from interfereing with med.marijuana and hemp. I see that as shifting the stress on DEA to find new ways to make their bread by busting herb affiliates. There will be more trumped up charges for smaller time operations, more confiscations of property on the flimsiest of connections to illicit activity etc. That will take time to build public outcry against it just as ever other modulation in prohibition has--now and in the 1920s with alcohol prohibition. I'm just worried the social tolerance for corruption is so high that we won't actually ever reach a tipping point.
In short, then, no, i don't think we'll see federally legal/decriminalized cannabis within a year.