The PC was an accident, which IBM repented themselves quite heavily, tried to regain with PS2 and failed to do so.
If the current trend of UEFI and laptops without any expansion options is any indication, that open PC of yore will fade into a very tiny niche, as computers become appliances.
The previous accident of that kind was UNIX. That's acute, considering an open-source is mainstream today - a couple of accidents is enough to change the world.
Yes, had Bell Labs not been forbidden to sell it, thus going to the market with a closed source OS, selling it the same price range as VMS, OS/360 and similar systems, the history outcome would have been quite different.
Still anyone that has had the pleasure to write portable UNIX code knows that portability is relative.
Maybe UNIX and PC wouldn't be enough actually, without at least four points (half-accidents at least) of that history - RMS, BSD, Sun and Linus. That's quite a fragile chain of events.
If the current trend of UEFI and laptops without any expansion options is any indication, that open PC of yore will fade into a very tiny niche, as computers become appliances.