I'm pretty sure that this has already happened, see: https://en.wikipedia.org/wiki/Plenty_of_Fish
Not quite 1bn (but 575mn in 2015 dollars) and mostly done by one person.
Also, "Plenty of Fish uses a Microsoft-based platform for itself, including IIS, ASP.NET, and Microsoft SQL".
2008 I think (from the wikipedia article). I met my now wife on the platform in 2013. I do think it counts, and it's important to note that even pre-AI, software has incredible leverage for small teams/individual people.
I'm pretty sure that this has already happened, see: https://en.wikipedia.org/wiki/Plenty_of_Fish
Not quite 1bn (but 575mn in 2015 dollars) and mostly done by one person.