It looks like the S.CO domain name changed hands at the end of last week or over the weekend. According to Whois records at DomainTools, S.CO is now registered to DNStination Inc., the proxy provider for MarkMonitor, a brand protection and domain registration company. As of right now, S.CO resolves to a generic GoDaddy landing page.
I believe S.CO was sold by GoDaddy / NameFind, although the purchase price for the domain name will not be revealed per GoDaddy’s policy. Earlier this year, Jamie Zoch reported that GoDaddy “acquired the premium domains held by the .co registry (likely ALL of the remaining ones they held)” via its NameFind business. There were quite a few single letter .CO domain names in that portfolio, including S.CO.
Back in 2012, S.CO had been used by Startup America, an organization that was co-founded by America Online founder Steve Case. At the time, it was announced that the organization would rebrand its url from StartupAmericaPartnership.org to the shorter S.CO domain name. It looks like the organization reverted back to StartupAmericaPartnership.org, although I am not sure when that happened. My guess is that the organization didn’t acquire the domain name from the .CO Registry.
According to NameBio, there have been
Google’s parent company Alphabet runs a division called 
Aron Meystedt, Director of the Domain Names and IP category at Heritage Auctions, emailed me about a portfolio of domain names his company is brokering on behalf of an undisclosed client. The portfolio is made up of approximately 750 one word and short .CO domain names.