On 1sld.com I published a report about the sales of 1-character short domains. Since 2013 the median sales grew by amazing 1073% on a steady growth!
The report focus is on the shortest possible format domains - 1-char short ccTLDs (contry code domains). This domains are very limited - each country can offer only 36 such domains in the Latin-1 charset and many countries reserved them. This makes them very rare assets. And they are also used by big tech companies for new shortening services and other stuff.
The 2018 report can be found here: http://1-single-letter-domains.com/news/news7/?reportr=2018b
