Pedantry activated: in my game dev circles, I've only ever heard .io pronounced "dot i-o" when talking about itch.io. The style, however, I usually hear as "i-o style" or an "i-o game".
Interesting -- if I see "open a .jpg file" I never hear people pronounce the dot, it's "open a jay-peg file". You'd definitely say "open an .exe file", again because no "dot".
On the other hand, "Microsoft .NET" includes the "dot", as well as "bought five .com domains". Yet in contrast, "bought five .edu domains" would usually be said without the dot.
Hypothesis: we don't pronounce leading dots unless for some reason they've become part of well-known "branding", like .NET or .com.
It was funny when Sun proudly and unilaterally proclaimed that Sun put the "dot" into "dot com", leaving it wide open for Microsoft to slyly counter that oh yeah, well Microsoft put the "COM" into "dot com" -- i.e. ActiveX, IE, MSJVM, IIS, OLE, Visual Basic, Excel, Word, etc!
And then IBM mocked "When they put the dot into dot-com, they forgot how they were going to connect the dots," after sassily rolling out Eclipse just to cast a dark shadow on Java. Badoom psssh!
On the other hand, "Microsoft .NET" includes the "dot", as well as "bought five .com domains". Yet in contrast, "bought five .edu domains" would usually be said without the dot.
Hypothesis: we don't pronounce leading dots unless for some reason they've become part of well-known "branding", like .NET or .com.