Re: Anything we should steal ? - Definitely
"Does Multics have any useful features that are not present in modern OSes ?"
Its virtual memory implementation comes to mind: in Multics, "files" were really persistent memory segments, i.e. all files were "memory-mapped" in Unix-parlance.
The concept was not without problems of its own (see the linked article above and the articles linked therein); but given today's availablity of reasonably fast, persistent mass memory technologies I think that exploring direct mass memory access while doing away with traditional file I/O might well be worth exploring once more.