It is, but just sitting can be a little deceiving in its brutal simplicity and I think some thought has to be put on the technique. I would often would just sit and think, not just sit. I wasted a lot of time sitting and thinking I am meditating. It's more like "just sit and be extremely watchful, alert". I also found it useful to have a timer nearby and evaluating how slow the time passes. The emptier the mind, the slower the passing of time. It also helps to tap into feeling the body, I would find that it's completely impossible for me to focus, if I do not have a good sense on feeling my body. Posture also plays a very important role. It's something to note that the average modern day person has posture that would take weeks or even months of focused practice to fix, especially one browsing this site. It's just sitting, but there are many things involved. * If you tell a beginner to just sit, they will drown in their own thoughts. Something more practical is, stare at the timer and try to not think, just perceive each second passing by, do not think, see how long can you last without a single thought **. Shikantaza is basically willful suppression of the thought process and pretty much the opposite of what the wikipedia article describes as a "similar technique" - "Do Nothing Meditation".

As for the article, I am actually doing 1 - 2 min shikantaza regularly while working. I'm staring at an empty screen. I do it multiple times per hour regardless if I feel focused or not.

* Don't try to fix the posture while attempting shikantaza.

** Obviously something even more practical for a beginner is to gain focus by counting breaths and then breath awareness, before trying the most difficult type of zazen. I'm just describing what would be a way for someone that does not practice to imagine what correct shikantaza feels like.