The article is misleading and the author has totally no clue on the complexity of user space memory management. Random on-disk virtual memory access will be a disaster if we just keep everything in so-called virtual memory without complicated cache mechanism.
Are you sure? PHK is a quite seasoned FreeBSD kernel developer and did phkmalloc which was used in FreeBSD for a long time, see http://phk.freebsd.dk/pubs/malloc.pdf.