4.0.x wasn't great but it was used pretty heavily.
It'll be slightly interesting to see it, and I'm not sure a more "popular" version like 5.0 would be much more interesting.
I'm curious about releasing 6.0 or 6.2, which MS was forced to recall because they "stole" some technology and put it in DOS. Although part thatd be interesting would be any damning code comments.