Vmware and other virtualization vendors as well as the various cluster computing solutions are capable of live process migration, checkpointing and a ton of other nice features that Plan-9 simply doesn't have because at the time it was to be an improvement on Unix and 'Beowulf' was still just the name of a character in a story, Amazon was a figment of Jeff Bezos' imagination and the Google guys were still playing with their Lego.
To really revive Plan-9 would imply diverting resource from a lot of projects that have progressed far beyond where Plan-9 has been stuck for well over a decade. So as much as I love the whole idea behind Plan-9 and the way they've made a better unix I fear that they will never be able to get the kind of push they need to gain parity. Pity, really.
Plan-9 could have been where Linux is now if they had caught the wind at the right time. Community is the single most important factor in whether or not a technology will succeed in the longer term or not. Linus Torvalds beat all of the incumbents by doing one simple thing: opening up the source right from day #1 when the barrier to entry was sufficiently low that he got buy-in from a lot of capable people.