&gt;&gt; Create a secure POSIX-compatible userland on top of seL4.
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&gt; This goal fills me with nerd lust.<p>I remember a L4 talk in which the speaker showed how more than 95% of the code of new OSes where devoted to being POSIX compatible and yet they 1) lacked a lot of features 2) missed many edge cases 3) had to modify their beautiful kernel design to accommodate POSIX use cases.<p>I think the only way forward is to do like Plan9 did. Just forget about POSIX and implement your own set of primitives (but first study what has been done in the last 40 years!). POSIX compatibility can come later with 80&#x2F;20 library that maps POSIX calls and behaviour to the new primitives.<p>And maybe POSIX is not needed at all. If your OS is interesting enough people will add #ifdef&#x27;d code for your platform, just like many UNIX-y applications do now for Android, OS X or Windows.