I'm going to have to disagree. Security is a pretty major issue, and anything that improves system security on desktop and server Linux is probably a win.
It's a shame that we will lose the simplicity of the plain-text syslog format. But syslogs are usually compressed using gzip anyway. So essentially for me, all this means is that I use <magic-lennart-tool> instead of gzcat as the first part of my shell command.
The big issue that I see is that a lot of system administrators will treat this as magic security dust, and not realize that they need to periodically save those hashes to a remote (and secure!) system in order to get any security benefit.
I also hope Lennart and co. realize the absolute necessity of backwards compatibility for the on-disk format. It would really embitter a lot of system administrators if their old logs became unreadable after upgrading to the shiniest new version. But assuming this is managed well, I don't see any reason why this couldn't be a good idea.
P.S. Providing a FUSE filesystem that can read these files is a good idea!