Faster no-op builds are always great, so let's see how this evolves. Jussi Pakkanen admits there is a dependency bug, so maybe things become slower when that bug (and similar bugs) is (are) fixed.
Assuming 0.04s is the all-inclusive "scan any transitive dependency file to see if it was changed since the last build", that's impressive. If there's a bug that results in only 1% of the dependant files being checked, then it's… well, useless right now.
Also, please don't forget functional requirements for a build system. See for example https://wiki.debian.org/UpstreamGuide#SCons for why Debian thinks scons is not a good build system. If Meson gets those things right, cool!
I haven't actually tried this, so it may very well be a very nice project. Just my thoughts when I read about a new and very fast build system. :-)