I remember when people used to make a lot of little micro niche blogs to rank well for very low competition keywords to make a lot of money on AdSense such as "4 slice toaster" and "yellow rain boots" Can people still make little blogs with keyword domains like 4slicetoaster .com and rank well on Google with a little bit about SEO?
It should be still possible but like trafficweb already said it won't be nearly as effective as it used to be. But on some keywords with a high CPC is still worth the risk.
A friend has a site selling only coffee makers and he is doing fine........ maybe it depends on the niche. I think a lot depends on your flair for marketing. If you can market in a way to attract visitors, then you may do well. A keyword on its own may or may not do what you need.