Yeah, I don't understand this either. I know that for certain cases FreeBSD has better performance, OpenBSD is possibly more secure, NetBSD more portable, but hasn't Linux proven itself enough at this point that these debates are mostly irrelevant? It's a decent UNIX like kernel, it's already used in Android and then obviously a lot of servers.
But what features or cabalities are you missing with Linux?
OpenBSD is simply a lot better designed than Linux, free from fancy bells and whistles. As the the world's simplest and most secure Unix-like OS, any mobile OS choosing it over Linux would have a significant advantage.
Android has bits and pieces of it, but not nearly enough.
Creator of the world's most used SSH implementation OpenSSH, the world's most elegant firewall PF, the world's most elegant mail server OpenSMTPD, the OpenSSL rewrite LibreSSL, and the NTP rewrite OpenNTPD. OpenBSD -- the cleanest kernel, the cleanest userland and the cleanest configuration syntax.
Those are some serious claims that are not at all objective. I can tell you that I have found OpenSMTPD to be at least as inelegant as just about everything else that touches mail, and PF is a good design but has always had serious competition from the commerical world.
I mean, I love OpenBSD too, but you can't drink the Kool-Aid like that. It's got just as many design tradeoffs built in as any other competent OS.
