Re: None of this changes anything
Transfering settings etc. between boxes - why? If you are in a "roaming" environment there is a central software repository with standard installations or a "default image" anyway (and that HAS all the settings since it is basically a backup) and the rest is done by the server storing your relevant profiles. If it is for backup - you can easily do that. The days of "tweaking the registry" died somewhere around the "days of the DOS extenders". OTOH the "guess where config file x is on distribution y" or even the "horde of config files" on Solaris are a PITA for most users
DLL Versioning is a problem with all dynamically linking OS, Unix/Linux is no better there. Requires lib x version a.b.c is a problem. Windows is smart enought not to kill newer versions. And multiple .NET versions can exist on one box
"Posix" is a combination of API definitions and tool definitions. And the API are abstracted away in the compiler libraries so I do not care (much). Non UI / non Appserver software is portable if necessary. More complex stuff is either in a language that does not care (Java, PHP), runs in an app-server or needs UI changes anyway (Try porting a Swing based UI to Android, join the "Nuke Mountain View" fan club)
Doing x for the sake of x (Real time is a good example) is stupid showmanship. RT, even more hard(time guaranteed) RT is extremly difficult to program and absolutely unneeded for 99.9 percent of the users. "Close enough" time shedules (That Unix and Windows can do) are more than enough. And those who do need RT - need a certified system and often are restricted to "use THIS". Been there, wrote the Fortran/Dicol and Step5 code.
As for ACL: There is some support for the older, withdrawn version that can be switched on/used. Under current Windows versions - they are on. Always.