They are referring to the upgrade from lenny to squeeze. So an in-place upgrade would be nice, but was not always possible in the past. As for 2.6.32, well, you really can't expect debian to support kernels from two releases ago, considering it was not always possible to support the kernel from the last release. And if you want to keep the in-place upgrade support and systemd -- for whatever reason -- decides to increase the minimal kernel requirement, you can always stick to an older version of systemd for the next release. However, considering that the first release of systemd was only in April 2010, it's not safe to extrapolate the fast development to the future. I'd rather expect the development to slow down as the important things are in place. And thus, an increase of the minimal kernel version is getting more and more unlikely. But of course I didn't talk to the developers, so I don't know their planning.There have been transitions in the past (such as udev) where the dist-upgrade should be performed as:
* Update sources.list
* Install new kernel and new udev
* Proceed with dist-upgrade
I have to say, systemd is really fast, I think it's the future, and that it could even be modularized after the development slows down. Even though my distro (Ubuntu) uses Upstart, I'd much rather have it. It was really worth the speed increase last time I installed it; and that was on a Pentium 4! I hope they pick systemd.